Well, here is the equation that you may know. CPU clock = multiplier X FSB. and basically, the FSB : RAM is set to 2:1. Now, seting FSB:RAM to 1:1, you can raise your FSB to 400Mhz max. Now think, if you have AMD rig , the mult are like 15.5 etc. So, 15.5 X 400 = 6200. So, you can OC to 6.2Ghz theoretically leaving the cooling or other things. Again, you can increase the mult in Black Edition ones. There is another fact that 800Mhz RAM ( corsair, OCZ, G Skill etc ) can be easily OCed to 950Mhz or so. And any 800 Mhz RAM are OC able to operate at 80-100Mhz more. So, setting the mult to 18 and FSB to 220Mhz you get 4.06Ghz ( while FSB:RAM is still 2:1 )
ONly if you want an intel CPU which have lower mults, go for the higher clocked RAM ( if you don't like to change the ratio to 1:1 ) Choice is yours.
As for the RAID support, My Biostar TA790GX 128M supports RAID 0,1,1+0,5.
Idea about RAID:
RAID 0 : defines a diskstriping scheme that improves disk read and write times for many apps. Min drives 2, max 6-8.
RAID 1 : defines techniques for mirroring data. Min drives 2 and max 2.
RAID 1+0 : combines RAID 0 + RAID 1 techniques. Min drives 4 and max 6-8.
RAID 5 : provides fault tolerance and better utilization of disk capasity. Min drives 3.
So if you have only 1 HDD, you don't need RAID. Better google about RAID to find the adv and disadv.