I'm just saying that workstation processors aren't built for your average motherboard, and sometimes, even your operating system. There have been problems with Opterons involving voltage in the past, but as long as you know what you're doing, you should be fine. Btw, your PS is a bit over the top for a 6800, but I guess you can never get enough wattage.
EDIT: Don't forget to make sure your new rig has a good cooling system. A Dual-Core Opteron (OCd) sitting beside a 550 Watt PS, with two HDs running like bitches just might cause some heat.