You need a 5400RPM Green drive.
For FRAPS recording, sequential write speed is where it's at... but since sequential performance arcs downward for HDDs as you approach the inside of the platter, higher capacities will work better.
Seek times barely factor in...
Take this F3 and F4:
Now lay them overtop each other. For highly sequential FRAPS recording, the F4 wins. It stays above 71MB/sec way longer.
Even a WD Green would be good, if you can find one on sale for cheap. (WD20EARS - WD Green 2TB - $70-75)