computer purchase advice needed

first off, i am an after effects guy who works solely on macs, so i need some advice for purchasing a 3D machine. the machine's main use will be running maya, and occasionally to run 3DSMax renders. basically it's a "which processor is better" question. i've configured 3 different machines and all fall within my bosses desired price range.
all 3 have pretty much the same components - 2GB RAM, NVIDIA Quadro FX 3450 256MB, 250GB system disk, DVD burner. here's where the choice comes in.
1) Dell Precision 670 with dual Xeon 3 GHz - $3555
2) BOXX 6200 with dual Xeon 3GHz - $3685
3) BOXX 5400 with dual dual-core Opeteron 265 - $3597

1 and 2 are very similar, so basically it comes down to which is better, Xeon or Opteron. now, this isn't a machine that i will, use, and our 3d guy says he really doesn't know which one would be better. basically i'd like to know which would be fastest/most stable in working in maya, and in render speeds. i figured the cow would give me the best advice. we need to make the decision within the day, so any advice is welcome.