The Ex3 will do fine displaying in a theater. I have shot and displayed a short with it used in a theater and it looks great. Honestly I believe any camera can look
great on-screen, but it depends entirely on the DP and the lighting. The camera may have only a 1/2 inch chip but if the DP understands the camera and it's limits, a great DOP can still be achieved, it just takes more time. Even more so, as long as you have a good story, your viewers won't care more or less what it was shot on.
The Canon 5D mark II like said actually can shoot some great stuff for a lot cheaper, granted you don't get the 24P, but again...most of the people that only care about that is US. The viewer could care less and you save yourself $6000.00.
Sony EX3
1/2 chip
4:2:0 color space
24P,30P,60I
Expensive Cards $300 + for 8GB
$8320
Canon 5D Mark II
Full Size Chip
4:2:2 color space
30P
Best low light camera I have seen btw
Uses Compact Flash
Can take advantage of Prime Lenses and all the fun that goes into it.
$2700
I own both, and let me tell ya...I am getting awfully close to selling my Sony if that tells you anything. The only drawback is handling the 5D takes some getting used to. Hope this helps.