First catwalkshoot with 70-200 2.8LII more difficult than I thought :)

Looks like you have all you need, but Dustman hit the nail on the head. Unless you were using HSS on the flash, the max shutter speed on the 6D is 1/180th. That would allow for movement of the, even slow moving, models to impact the IQ.
With the 6D, you can easily bump the ISO and go without supplemental flash. Most of the model shoots I have seen, were lit up to a point that no additional light was needed. And in some cases, the flash was not allowed by the event anyway.
Bump your ISO to 800 or so, go to 5.6 and shoot around 1/500th and your shots are going to be 1000% better just using that combination. You can still bump up the Aperture if needed for deeper DOF on more than one subject shots. THe 6D is very forgiving on ISO, so don't be afraid to let it go higher if needed to get the DOF you might need.

Thanks for the updates on language by the way, everyone. I'm a native English speaker, but I do live with a local dialect and I like to learn and understand words from other regions. I had a sense that a 'catwalk' was a 'runway' and I can see (and enjoy) that both words have more than one meaning. Here is the US our show is "Project Runway" with Tim Gunn and I wonder if all the rest of you are watching "Project Catwalk" and do you have a host as fabulous as Tim?

TeamSpeed wrote in post #17183578
Be careful, there are indeed times to shut off the IS. For example once your shutter speed exceeds your focal length (or twice your focal length if you want to be conservative), you no longer need IS, and in fact IS can cause grief. If you are trying to stop motion, chances are your fast shutter speeds are more than adequate to eliminate the need for IS, and if you just want to aim and shoot, sometimes waiting for the IS to spool up isn't an option, and that "spooling up" can hurt your images, blurring them, etc. I never have IS on at ball games, for example.

while i don't doubt that you're right, i must say that out of 10's of thousands of pictures taken with IS lenses, I've never noticed blurriness that I attributed to the IS system. i have also done events with the 70-200 IS II in question where i took shots without letting the IS system spool, and i did not notice any blurriness. and i am definitely a pixel peeper.

is the effect extremely subtle?

to the op--i vote to never turn off IS unless using a tripod (i have noticed strange effects due to IS on tripods). but i guess there's teamspeed's comments to consider as well.

yogestee wrote in post #17183412
I've always known it as a catwalk also. Where I'm from there are catwalk models who specialise in this kind of modeling as opposed to photographic modeling.

Right Said Fred lyrics

I'm a model you know what I mean
And I do my little turn on the catwalk
Yeah on the catwalk on the catwalk, yeah
I shake my little tush on the catwalk

Read more: Right Said Fred - I'm Too Sexy Lyrics | MetroLyrics

Xyclopx wrote in post #17188740
while i don't doubt that you're right, i must say that out of 10's of thousands of pictures taken with IS lenses, I've never noticed blurriness that I attributed to the IS system. i have also done events with the 70-200 IS II in question where i took shots without letting the IS system spool, and i did not notice any blurriness. and i am definitely a pixel peeper.

is the effect extremely subtle?

to the op--i vote to never turn off IS unless using a tripod (i have noticed strange effects due to IS on tripods). but i guess there's teamspeed's comments to consider as well.

This has been my experience both of an on. One the SS gets up to a high enough value the IS is too slow to cause any blur (on or off a tripod) Although I haven't tested this to the extent I have IS on tripods at less than 1/4s.

I being a novice find the IS on or Off argument a constantly odd one. TS seems to bring up what might be a valid point. But I have heard/read that leaving IS has minimal impact to most shots and even though unnecessary when SS is high enough that it helps be stabilizing the OVF whenever you are on the long end of a telephoto lens. And yea, I too have seen weirdness when IS is on while on a tripod.

ejenner wrote in post #17188818
This has been my experience both of an on. One the SS gets up to a high enough value the IS is too slow to cause any blur (on or off a tripod) Although I haven't tested this to the extent I have IS on tripods at less than 1/4s.

The Canon IS system might be smooth enough that when it activates and your shutter speeds are fast enough to not need the IS, it doesn't have the effect you would see, despite Canon's warnings about IS they have in their documentation. With 3rd party systems, however, they may not be so smooth, like the older Sigma OS systems, they will twitch a bit and I expect you might see those systems affect your images.

I guess I couldn't see a reason to EVER have the IS on when in a studio setting with lighting and flash controlling the light, especially if using a tripod. I would save the IS wear and tear, as well as the battery life. That is just me though, I try to teach my young-uns to turn off stuff they aren't using.

K Soze wrote in post #17188768
Right Said Fred lyrics

I'm a model you know what I mean
And I do my little turn on the catwalk
Yeah on the catwalk on the catwalk, yeah
I shake my little tush on the catwalk

Read more: Right Said Fred - I'm Too Sexy Lyrics | MetroLyrics

Hahahahaaaa..

https://www.youtube.co​m/watch?v=39YUXIKrOFk

TeamSpeed wrote in post #17188869
The Canon IS system might be smooth enough that when it activates and your shutter speeds are fast enough to not need the IS, it doesn't have the effect you would see, despite Canon's warnings about IS they have in their documentation. With 3rd party systems, however, they may not be so smooth, like the older Sigma OS systems, they will twitch a bit and I expect you might see those systems affect your images.

Was unaware about Canon's warnings, I have to admit. I also don't have any 'old' lenses and the 24-105 is not used by me in that way. I can imagine some older IS's not being as 'nice'

Agree though that with 3rd party lenses I'd be more vigilant about it. I only have the 18-250 with IS and that's not exactly a 'sports' lens either. I wouldn't trust it to focus fast enough to be able to get a shot in while the IS was activating.

On the subject of IS, I find it interesting that Canon has sort of split the IS into 'old' and 'new' at some point. However it seems to me they are constantly tweaking it. For instance the IS on the 100L is definitely different than the 70-200 f4 IS (and not just the 3-way motion or whatever it is) and the 16-35 f4 IS is different again. They all behave quite differently on tripods at slow SS too. The 16-35 actually does shut of on a tripod after a shot period of time - maybe 1-2s (actually you can still hear the motor, but it really doesn't move at all). Not so for the other lenses I have.

No doubt, they have indeed been working on the IS systems, from the hybrid systems to tripod-aware IS. This is why the 100-400L is in such dire need of being replaced, it is the very old IS system, and just imagine if the 100-400L had a nice IQ upgrade and a 4 stop IS system. It could sell for around $2000, I suspect.