Honestly, for a stationary and well lit subject, you are going to be using a tripod and ISO 100. You aren't going to really notice an improvement going to anything from your 20D unless you want to print huge.
For shooting a bit of everything, including action, I'd have a hard time choosing between a new 7D and a used 1dmk3 if had up to $2000 to spend on a body. Although, I'd probably end up going with like a 50D and $1100 worth of glass instead.





