Well, firstly, when i was talking about the 16MB cache 5,400rpm drive, i wasnt talking Seagate. But the average 5,400rpm isnt really very loud anyway, so it dosnt really matter anyway. 7,200rpm is louder, but not really by that much. I hardly hear my notebook hard drive and it's a 5,400rpm.
Secondly, Notebook hard drives only do around 20mb/s - 30mb/s transfer rates. There is no way that they could do over 90mb/s. Hell, that's just under what my Raid 0 configuration of Raptors do and they're 10,000rpms.
Normal desktop drives do around 40mb/s - 65mb/s depending on brand and type (assuming they're all modern 7,200rpm drives)
But in a notebook drive, there's a tiny difference between 5,400rpm drives and 7,200rpm drives performancewise.
For $100, that's not worth it.