Should be powerful enough, no probs unless your doing some realy heave stuff!

Think I would go for the NVidia as thats defo quailfied by Alias (check out the charts on their website)

I personally dont know about the Opertron and Xenon's, if you have a look on CG talk theres a thread showing the fastest PC's of the CG talk users with regards to rendering times with a set file. and I think that opertrons were at the top (they were dual opertrons, not dual core but duel processor) so you might want to have a look at that to gather some info before commiting.