I would not be so quick to jump into a hardware RAID. Make sure your
hardware is supported first. I have a similar system and my hardware
RAID is not supported at this time.  I am currently using a software
RAID. As for most stable GNU/Linux i would have to say Debian
http://www.debian.org/ even though i am a hardcore Gentoo
http://www.gentoo.org/ fan! You may be interested in some tutorials i
have on my site http://infectious.cc/ good luck with the hardware
RAID!

-- 
-Ryan