I would agree with fat foresters stuff. 320gb from samsung or WD if your not looking for that much space. Why do you want 32mb of cache? It makes virtually no difference at these capacities, I'm not even sure if they make one w/ that much cache under 500gb. It won't make a difference until your around the 1tb range.
About the one rail, here's our very own pancho's take on it from our psu guide:
Rails: While many psu's are multi rail, it is better to get a single rail system because with a single rail, the psu can transfer 100% of the 12v output of the psu to the computer, whereas in a multi rail system, you can face up to 30% distribution loss due to underutilized rails. lets say for example lets say rail 12vr2 is assigned to work for the cpu, and lets say the rail carries 17Amps of power, but the cpu only uses 7A of power, that 10amps in lost, whereas in a single rail system, the system draws from only one rail so the power loss is not there. also, lets say you have a grafix card that required 20A, but the rail its using is 17A, you have instability and problems like that, thats why for a sli/crossfire system, you definently want a single rail psu, because everything draws from the single rail, which has all the power of the psu. whereas if you're trying to sli/crossfire on a quad rail system, which has like power of the psu split up, that 1/4 of the power of the psu might not be able to power the sli/crossfire grafix cards.