I have all Maxtors mix group Ultra 133, PATA 133, SATA 150, 5x 60GB, 1x 120GB, 3x 200GB, 1x 250GB, 1x 300GB, 1x 320GB these are in 4 built boxes some have more than 4 HDDs in them. But Frankly if you cool the case correctly you shouldn't have problem with 500GB with heat..
Example: 320GB would be 298GB free to use.. where as a 300GB it would be 289GB free. 200GB is 189GB free only the 120GB there it's only 114GB free. 60GB are 57GB free.