IMO, unless I'm trying to break overclocking world records, RAM speed doesn't matter much to me nowadays. I don't even notice a speed difference. So I try to get the most economical mainstream RAM (i.e., low price) with decent speed ratings. For my Core2Duo setup, it was DDR2 800MHz with decent timings. For the i5, I grabbed DDR3 1333MHz. I don't plan on doing much overclocking. In fact, I'm thinking about UNDERvolting the CPU since this is a quiet HTPC setup. I think I notice more responsiveness with faster hard drive or SSD than I do with RAM.
SATA II is definitely getting saturated with SSDs getting faster. To get the full bandwidth, one must resort to external controller cards (i.e., Fusion-IO
).