well there are tradeoffs. If you want low power and high performance, you come down to choosing between either SSDs (very expensive) or a lot of laptop drives (cheap, but higher latency; throughput for something like video is fine though as you can fit a lot of them in a chassis; switching from 8drive Z2 groups to mirrors gets you a 4x improvement in throughput, which completely negates the throughput disadvantage of 5400 vs 7200).