I've got a 2TB WD Caviar Green and a 2TB Samsung HD204UI in mine. I'm certain that it can handle two programs recording and a third playing back without a hitch. I don't know that I've seen it recording four and playing back a fifth at the same time.
The 7200-rpm drives are noisier and hotter than the 5400/5900 rpm "green" drives. I put a 3TB Seagate Barracuda
in my gaming PC a couple of months ago for $140.
i7-4770K, H70, Gryphon Z87, 16 GiB, R9-290, SSD, 2 HD, Blu-ray, SB ZX, TJ08-E, SS-660XP², 3007WFP+2001FP, RK-9000BR, MX518