Given that recorded TV can only live on one partition and I dont like RAID in my VMC I went for a 1tb = 930GB usable for recorded TV. (Nearly ran out of space during the olympics

) I also keep weekly images of my sys partition on this disk.
My system lives on a separate HDD which has 2 partitions, one for sys and one for other media.
The logic is to keep disk intensive recording on a dedicated HDD and low intensity stuff on the same physical HDD as the sys. I use a samsung eco-green 1tb for recorded tv and it will happily cope with multiple simultaneous recording and watching activities.