Rebel backup?

I'm transgressing into the more professional aspect of photography and was wondering are any of us pros out there using Rebel bodies as a backup? I'm shooting with mostly L glass and have a CHDK-hacked Rebel 400d / XTi I've been using as a backup.

I replaced most of the electronics and the shutter was replaced and it has about 400 clicks on it. Honestly I can barely see the difference between this and my 5D Classic.

I do like to use the 50 1.8 Mk.I as a low-light sidearm.

Hmm, hard to answer the question! Since you have the Rebel, well, having it as a backup is better than no backup at all, so a "bird in the had" beats a bird in the bush!

Of course, where the 400D will struggle is in low light situations where you can't use a flash and have to up the ISO to 800 or higher. I don't know how much indoor "available light" scenarios you've shot with the 400D, but in the bit of testing I've done with the 400D that I bought for my daughter a few years ago, noise at ISO 800 was beginning to be a problem. And, with wedding shooting, the need for available light shooting will arise.

But again, you have the Rebel. Have you been considering alternatives? Any suggestions from here will add up to newer equipment, which can be spelled $MONEY$!! So, fill us in a bit!

I noticed a huge difference from my 40D to 5D classic (also had a 400D, 20D, 30D looked the same as the 40D to me.) The 5D is sharper out of the camera (I hate PP) the main difference is my Sigma 24-60 which was OK on crop but quite nice now on the 5D.

Anyways, if your rebel is strictly "backup", or even as a second camera if it works for you, keep it! If you want to do weddings or something where you are using each camera attached to a double-R strap with different lenses on each, well that is a different story and perhaps you want to upgrade (or not). Again I must say I notice little IF ANY difference in IQ from my 400D to 40D, and kept my 30D over the 40D cause I could sell the 40D for more money at the time.

Seems to be the general consensus. Above 800 it can be noticeable but a minor noise reduction in PP helps.

I've strictly used it for two things, low light tele with the 50 1.8 and super-tele work with nature scenes or anything I need length. I'll hold onto it until something better falls in my lap.