The new Opterons are socket 939 and do not require registered memory. The best socket 939 motherboards are all SLI though so there is no way to get away from that unless you want to go with an infeiror board. The Asus Premium is still a good choice although i'm waiting for the new A8N32 SLI to come back in stock. It has far more advanced features than the Premium including 8 phase power. There are lots of
reviews of it floating around out there. It's certianly worth a look. The only problem is actually finding one in stock lol. They should be back by the end of the month if you can wait.
For pure overclocking goodness you can't beat DFI. All the current world records for AMD overclocks are on DFI boards.
This one is the current king of overclocking.
I'm not so sure about the hard drives. I have 2 Raptors in RAID 0 and I can tell a difference over just running a single. Some things load faster, especially game levels and windows. Yes RAID 0 is overrated and probably overused... but it's still the faster than a single drive; even if marginally. When you're on the bleeding edge every little bit counts eh?
Sounds like you have a really nice build in the works, have fun with it and let us know how it turns out