Well I did just that. My 40D took a turn for the worst so needed something to fill untill I can get hold of a 5DMKIII. So I got one a year old under 10k shots for £750. Have to say the camera is incredible, everything is great but...
and its a big BUT! The IQ and noise are horrible in the places you don't expect. In fact I am impressed how good the ISO performance is over 1600 (as the 40D was unusable over 1600) but up to 800 it is horrible! 100-400 really really disappointing, especially 100!!! Coming from a 40D it was much cleaner, its still working to make a comparison and shot two side by side and the 7D is worse, noticeably worce. The DR has no difference either... so where it counts it was disappointing, and i was expecting it to be better especialy DR i thought the IQ would be similar. Everywhere else it is an awesome camera the AF system makes the camera useful for everything and the 8fps is great too, but now after 2 weeks im thinking of just selling and biting the bullet for the 5D MKIII and converting FF.
On my 40D I didnt use any NR at ISO100, on the 7D im using 5-10 on the slider and loosing detail. The NR is set to standard too. Its ridiculous, I was using 5-15 for 400-640 on the 40D.
Maybe I was expecting too much but was a bit disappointed. Not just my cam either have tested two to make sure its not just mine.
Is this normal from you other 7D owners. I hate dissing this camera as im a true canon guy, and ive heard great things about the 7D.I remember hearing another member being upset about the ISO100 performance and thinking he must be mad. But I really feel strongly on this one.
The 7D is a great camera - but as you said it has a lot of noise in low light. In good lighting, it isn't so bad. For sports, the 7D is excellent. High FPS, extra reach with the crop, great AF. I also picked up some of the faster non-L primes for indoor sports - 85 f1.8. The 7D allows you to get shots you otherwise wouldn't be able to.
I was initially a bit disappointed with the IQ when I first got the camera, but have grown to love it after I have learned what light it works well in and not. I shoot 80% sports, so beside stepping up to a 1D body, the benefits of the 7D far outweigh the compromises for me.
However, if I did not shoot a lot of sports, I would not buy a 7D. I think there are better choices for general purpose shooting, landscape, etc. A 60D or T4i would be less money and probably better - or go FF. A 5DIII gives you just about everything a 7D provides (and more) except the reach of the crop, - so if that is in your price range it seems like the way to go, short of a 1D body.