I would say a properly built PC may not ever need RR unless you have a session with so many tracks that 1 drive chokes. I personally have yet to hit that wall with 60+ tracks, but others that use 100+ may have a different opinion. I would ONLY be looking at i7 950 and up cpu's and a socket 1366 X58 mobo for best performance. If you ever DO use RR, be very careful about backing up your session properly as you will have audio files on 2 drives
(I have enough trouble keeping track of everything on 1 drive
). BTW, your best performance will be on SATA internal drives(eSATA SHOULD perform the same, and both are mush faster than any FW or USB drives).