I recommended http://www.dpreview.com for a side-by-side comparison.
The main difference between the 40D and 400D is that the 40D has better image quality (somehow, despite using the same crop factor and CMOS sensor as the 400D). But it can do 6.5 fps, whilst the 400D can only manage a meagre 3 fps.
Yes, the 40D can take all the lenses we've discussed so far. It has both EF and EF-S mount, just like the 400D.
Hahaha. I think you can only decide for yourself when you've tried out both cameras.
Oh and yes I'm pretty confident the 50mm and 85 mm f/1.8s can manage the low light conditions.
Thanks again for responding unseenshadows.
Did some comparisons at dpreview last night. Yep saw the 6.5fps. Yes I need to go and 'try' it at the shop. Maybe vivo city. Saw them lined up the cameras for anyone to have a feel. But I doubt one could actually start shooting with it there & then. Really like the rugged texture on the 40D and if its going to keep me company for the next 3-5yrs, I want something that feels good while I am shooting and I could improve along with the recent technology thats available. The 30D is not that much cheaper. How strange can that be!?!
Yes the two prime lenses f/1.8 will be at the top of my list. Just wanted to make sure I have at least one walkabout lens (for my weekends) as its not everyday I get to attend exhibitions.
I am still pondering over what you wrote previously when I mentioned about the Sigma 17-70mm F2.8-4.5 DC Macro:
"At 70mm that lens is 4.5 wide open and can't perform at low-light conditions. 17 mm at f/2.8 would also be too wide an angle for your indoor photography of exhibits."
Compared to Tamron 17-50mm f/2.8 (zoom):
I think you meant, the Tamron will only shoot at f/2.8 in the range of 17-50mm.
With the Sigma 17-70mm f/2.8-4.5, it does not shoot 70mm at f/2.8?