My suffing of the web has suggested a XEION procressor. But never dealing with INTEL processors before I really have no clue as to which one would be best. As for the budget. I know it's going to cost over $1,000 (possible in the $4,000 range).
I forgot to mention two important spec.
1) The procressor has to be 64 bit
2) The MB has to handle at least 6 SATA(3 if possible)/SAS diskdrives. In a RAID 5 conf.
The CAD software in am using is ALIBRE ( WWW.ALIBRE.COM ).