So full frame might just be it for you! Do you find your kit lens to be wide enough in room shots, just not fast enough?
The kit lens is wide enough for room shots, it's just not fast enough like you stated. If I bought the Canon 5Dc w/ Canon 28-135, I think I'd be fine with that combo for now. I'm a bit worried though, many people complained that on a FF body, the Canon 28-135 is soft in the corners.
Yup, you nailed it. You def need a specialized wiiide lens, whether you're using cropped or full frame.. your 18-55mm on the T1i is about the same as 28mm on full frame, so you'd need to go to at least 24mm on full frame to do better. If you don't mind the wide-itude of 18mm on your T1i, then the 28mm prime, or that Tamron 28-70 I mentioned (but it sounds like you probably should look at a wide prime over a 2.8 zoom) should be OK. Otherwise, you'll find 28mm lacking, too.
I don't actually have a problem with the 18mm on my T1i, in fact I think it's really wide for my taste. I do like that focal length. So I'll stick with you suggestion of getting the Tamron.
But my main concern is, for the 5Dc, the shutter count. That camera was like $3K when it came out, so it was probably mostly pros buying it, which means lottssss of shutter actuations. I've seen listings of 5Dc's that explicitly mention they've had their shutter replaced. That's a goood thing! : D Look for that (or ask..)
I've been looking into all of the Ebay listings, Amazon listings, and Craiglist listings for the shutter count. If the camera was recently serviced, I wouldn't mind paying about 750. If it hasn't been serviced, or has a high shutter count, I'd barter for about $600.
-Side Note: If I replace the shutter on the 5Dc, does that mean I have a new 100,000 shutter life?
Let's not beat the dead horse again, in terms of image quality, 5D will smoke any APS-C camera ever made.
He must be smoking pot. I find 5Dc's ISO performance a lot better than 50D.
... Aren't you guys both praising the 5Dc haha?