Longboarder - For an SLI motherboard, try the one I was going to originally include in this build; ASUS P5B Deluxe
. Its not that much better than the P5B-E, but if you want SLI and some other goodies, go with this one as its actually one of the cheaper SLI motherboards.
As for RAID 0, it DOES increase data access rates. You have to decide whether its worth it to you to get two drives for the storage of one, but faster speeds. The performance granted with 10K RPM HDDs is a little greater than a RAID 0 setup, but the HDDs also cost more, and don't give quite as much storage room.
Sidenote: I'm not very well-read on Master/Slave setups, they were...before my time. However, with SATA HDDs, there is no Master/Slave designation. Each HDD is it's own. So basically with SATA, you would not be keeping the data on a Slave HDD, just a seperate HDD.
Also note that the P5B Deluxe has 7 SATA ports, but only 1 PATA port (2 devices on one port). So you will only be able to connect 2 CD/DVD drives or 2 IDE Hard Drives, or one of each.