I have a 8 core Mac Pro 2008 that I use as a backup machine and for 3d rendering. It's got two GPU cards and 32 GIGs of RAM, so there is a little extra investment in the machine. It currently runs at 2.8. Is there a worthwhile CPU upgrade path? It will not serve as my main machine, but I'm always evaluating how best to invest in more rendering power. If I could get 40% or better improvement for around $400-$500 and not a huge fuss I'd think about it. Possible?