@daviesgeek Yes, put the fastest spinning drive you want, something like a 10k RPM VelociRaptor on a SATA 3 bus (6Gb/s) and it won't go any faster than it would on a SATA 2 bus at half that speed, in fact even the latest ones will struggle to push past 200MB/s
USB3 would have to put in less than a 3rd of it's theoretical speeds in real life to cater for the fastest spinning disk in the world, and most are considerably slower than the VelociRaptor tomshardware.com/reviews/velociraptor-1tb-hdd-ssd,3250-4.html
@daviesgeek I put one in my stepsons gaming rig, I built it when the floods made hard drive prices stupid, but luckily (!) for me Best Buy UK went bust, and I managed to pick on up at 66% off, which made it almost reasonable!