OK, insert arrived today. EASILY fits the 3 lenses mentioned with a body on any of them. It's slightly bigger than I needed in width and depth, but I needed this size to get it "tall" enough for a 100-400 on camera:
I brought this pack in today to see how it'd fit:
the insert fits in PERFECTLY... There's only 1 issue... The side zippers don't go all the way to the bottom... Plus the bag is taller than the insert, so when it slides down, the center of the insert (the LCD on the body) is right where the zipper ends. I'm not worried about the camera short term (I have a ZAG LCD cover) but yeah, not ideal. Beyond that, it makes it tricky to get the camera out of anything but the top tube. I could always keep the camera in the upper slot, but yeah, I might be looking for a bag (see below) with a zipper that runs the whole way down, OR having someone put in a longer zipper, or even slide this one around (I don't need it running down the other side).
I am really considering the moved zipper idea though, because this bag is so slim and so stealth you'd NEVER guess there was that much gear in it looking at it loaded. It looks like a lightly loaded backpack for school....
if that doesn't work out, then this is my second option:
of course the burton isn't without it's own issues. The pack is a bit shorter which is an issue as I'm 6'4". So the sternum strap is basically a chinstrap when slid ALL the way down.
Beyond that it's got straps galore on the back to carry a snowboard vertically or the blade to an avalanche shovel. If I were to use this pack regularly as a camera bag I'd have to cut off the straps. I wouldn't miss them as I have another better BC skiing/riding backpack, but I just feel weird about cutting things off. If I could unstitch them and restitch them I'd do it w/o a problem, but yeah.... I'm not even 100% the zipper goes all the way down, but I'll be playing with this tonight.
Both packs also have stitched on waist belts. I'd prefer something I could keep in a pocket until needed (crumpler) so I might cut those off as well and sew on those plastic loops to use as needed.
Basically, this is where I'm at:
- the dakine fits me better
- the dakine's zipper doesn't go to the bottom
- the dakine's waist belt is sewn on
- the burton doesn't fit me as well, but fits the camera block better
- the burton has way too many extra straps and a shovel pocket
- the burton's waste belt is also sewn on
- the burton is a better colorway (almost all black with some red accents)
I'm half thinking i need to find a good seamstress (but for this material?) and have them move the zipper on the DaKine AND remove all the BS from the Burton.

all in the pursuit of perfection I guess. I'm also thinking I might end up selling the Kata though....