Thanks for your suggestions. I'll think about it a bit more, but I think I'm going to just hold on to the cash for now and upgrade the GPU and RAM as you suggested. I'll try to get another good year out of it and build a brand new one next fall when I have a $1800 budget or so. If the GPU and RAM improvement don't impress me enough, I'll probably jump on building a new rig earlier. I can always return them within 30 days.
One additional question about the HD 7950 - do you think its worth getting two of them and crossfire them?