Apparently the fastest 7200rpm drives at the moment are the single-platter 250GB drives, as having one platter means the arm for the heads is much lighter than

Apparently the fastest 7200rpm drives at the moment are the single-platter 250GB drives, as having one platter means the arm for the heads is much lighter than say a terabyte drive (4 platters) or a 750GB drive (3 platters) and can therefore home in on the appropriate drive track more quickly. Not useful if you need lots of storage though. 750GB drives are definitely the most value for money at the moment.