Well, if you want to pull the trigger right now, I'd say the EVGA SR-2 motherboard, paired with a duo of LGA 1366 Westmere CPU's is your best bet. But, as seen in a news blip just a few days ago here on Tom's, Intel is gearing up to launch a whole slew of new Xeon CPU's in to the market in Q4, for the upcoming LGA 2011 interface.
If you can wait, I'd hold off to see how the new Xeon's shake out and what kind of performance they'll offer. Personally for me, I couldn't wait, since I just built myself a decent workstation/gaming rig around the Xeon L5640 Westmere hexacore and while I haven't played with anything like keyshot yet, I gotta say that this thing is damn fast for anything else I've thrown at it.
I might have to wait...but I want to know more about your rig as it sounds like what I am trying to do.
What hardware do you have in it and what is the Xeon GHz at (2.26 I believe unless u can overclock it)?
Do you have a gaming or workstation card in it?
I am hoping to findout that I can put both type of cards on a single mobo somehow.
You could really help me out and provide the forum some neat specs by testing your rig with a trial of keyshot.
We then can compare the differences of my i7 firstname.lastname@example.orgGHz to your server cpu build.