Which body to use with 300mm f/2.8 IS II?

I am renting the Canon 300mm f/2.8L IS II for an upcoming air show, but I have a decision to make regarding the camera body to use and I am hoping to get some opinions from the community. Essentially I have 2 options:

1. Mount the lens on my 7D, which due to the crop sensor turns the lens into a 480mm with the ability to shoot wide open a f/2.8.

OR

2. Mount the lens on 5D mkIII with my canon extender 1.4x III which turns it into a 420mm f/4.

In the past, I have shot air shows with my 7D and my 70-200 f/2.8 with the 1.4x extender and have been pleased with the focal range, so I don't think the difference between 480mm and 420mm is an issue for me. I guess it really comes down to image quality and whether the sensor on a 7D will give me better results at f/2.8 than the 5D Mk III at f/4 using an extender. What would you all do?

Just thinking out loud, but Im pretty sure 2.8 wont be necessary (all things considered).

If I were you I would use both bodies. I have a big prime (400 f2.8), and I also have a 1.6 crop body and a full frame body. I usually have both bodies with me, as well as the 1.4 extender, and sometimes the 2x extender. If you have both bodies with you, as well as the 1.4x, you have the following effective focal lengths available at your fingertips:
300mm f2.8
420mm f4
480mm f2.8
768mm f4

This gives you a great range of focal length flexibility, with the IQ benefit of using a big prime lens.

If you have all that gear, why not have it all on your person at the air show? I have this much gear, but an even bigger, heavier lens - and yet taking all of this with me while backpacking over mountainous terrain, across rivers, etc is not "too much to carry". And I am not by any means a big or strong guy. It shouldn't be any problem at all to have both bodies with you for the duration of the airshow.

Another vote for shooting with both 7D and 5D3. It'll be interesting to see how 7D vs. 5D3's better AF, but, with 1.4x TC compares.

I would personally use the 5dIII,

Apply a 1.1 crop factor to the 420mm image and it becomes 462mm, and you still have 18mp left.
Shooting a 1.4 converter on the 300 f2.8 IS II doesn't noticeably degrade image quality to my eyes.

The pixels of the 5d3 are bigger than those of the 7d, so the apparent sharpness of the naked 300 on 7d could be very close to that of the 5d3 300+1.4, I would still bet on the last to provide sharper pictures., furthermore the ISO capabilities the 5dIII supposedly is around 1.4 stops better.
So the loss from 2.8 to f4 should not result in more noise.

Then the more advanced autofocus on top of that, the only thing I think the 7d surpasses the 5d3 is in frame rate.
Airshows are not most demanding on autofocus, so the 7d will do just fine there.

Maybe use the 5d3 with 1.4 converter and 300mm
and the 7d on your 70-200?, you can always switch during the show when you want more reach/wider shots

5D3 with 1.4x should give better image quality between those two options.

http://www.the-digital-picture.com …omp=0&FLIComp=1​&APIComp=1

That said, what about a 400 5.6 or 100-400 5.6 on the 7D? Should save you a bundle of money and would probably work out better than the 300 2.8.

Heck yes! Take both.

Put your 70-200 on one and the 300 on the other.

I use a pair of 7Ds that way a lot, 1.4X with the 300 some of the time, too.

It's a lot faster to switch cameras than it is to switch lenses. And there's usually plenty of action to try to keep up with at air shows.