Re: T3i vs 5DMK2 (Video Only)
 

There are many occasions where it's not possible to use an off camera lighting kit e.g. in church, run & gun documentary etc. In any case low light performance isn't the only advantage of the 5DII. Good wide angle lenses are another. Build quality & superior still photographs are others. All in all a 5DII is my first choice camera with a 600D as my second choice. Here in the UK the difference in price is only around £1000 i.e. about $1500 although putting that in perspective it means that you can buy three 600Ds for the price of one 5DII.

Re: T3i vs 5DMK2 (Video Only)
 

Jumping a little late, but for me the 5d2 was worth the extra expense. The quality of construction, controls and the pro shutter make it a better long term investment. You'll get a lot more clicks out of the 5d2 than any of the lower cost models. The rear jog-dial is a must have, no more video game controls for me on a DSLR ... though they are fine on something like the NEX or the Fuji X100 that I use as walkaround or B cameras tot he 5d2. The extra sensitivity and less noise are a big for me as well since I like to frequently shoot wide and in natural light - the FF sensor allows you to take full advantage of the lens' FOV and aperture. So while the cost of the t3i body is lower, a lens that gives you the FOV of a fast 35mm or 24mm will cost quite a bit more, and in many focal lengths it just doesn't exist. I just picked up a Zeiss 21/2.8, which would be a grossly overpriced 34/4 equivalent on a cropper. The 35/2 is half the cost of the 21. That $900 difference is more than half the difference between the 5d2 body and the t3i body. When you start investing in fast glass for specific FOV's, the price gap narrows pretty quickly. I guess it depends on your needs if there aren't budget restrictions. If I shot wildlife I'd buy the 7d. The added cost for pro construction and a FF sensor is worth the investment.

Re: T3i vs 5DMK2 (Video Only)
 

Disregarding video quality and which one's better and if they're the same, a canon 5D MKII is still going to be working 10 years from now and It's going to hold on to it's value pretty well. A T3i will maybe last 3 years with standard usage and if it is still working in 10 years, It'll make a great paperweight.

Re: T3i vs 5DMK2 (Video Only)
 

I agree with Chris. Want to use primes? Get the 5D2. You can get fast set of primes from wide to medium tele. Want zooms? Get a crop cam. You can get an 11-17 as well as a 17-55/2.8 with IS. Can't match that on the 5D2. (The 24-70/2.8 has no IS.)

One thing that confuses me is why to shoot at 1600 ISO? The low noise settings on the 5D2 are 160, 320, 640, and 1250. If you must, go for 2500 ISO, rather than 1600.

Of course, everybody has their own feeling about how much noise is too much noise depending on their projects, their monitoring, and their personal preferences. Some shoot at 6400 ISO and are thrilled that they can use so little light. Others won't go one stop over 160 ISO, preferring to burn watts rather than see noise. Some use noise reduction regularly. Others won't touch it. We might be able to measure noise scientifically, but tolerance for noise is subjective.

Re: T3i vs 5DMK2 (Video Only)
 

Let's be fair here. That's a bit of an exaggeration, no? My Canon Rebel XT from 2005 is still working great -- plenty of wear and tear. And there's no way that's a better built camera than the T3i -- or am I missing something.

Re: T3i vs 5DMK2 (Video Only)
 

We have the original 300D and I've put it thru some seriously tough conditions, and it still works fine after a shutter replacement, so that the T3i won't last 3 years is just bogus.

We still also have and use a 350D, 400D, 20D, 1Ds, all much more than 3 years old. The pro bodies are expected to last, but the consumer bodies are not junk.