I didn't know they had 4Tb drives now.
I have two of the Deskstar HDS721010 1Tb drives now and I'm pretty happy with them (that's why I bought another this month.)
I once read that larger drives are slower (given the same cache,) so it would be good to have the OS on, say, a 100Gb drive (assuming SSD is not an option.) Is this true? If so, is it any better than a 100Gb front partition on a large drive? My question assumes small partitions would be used for the OS, not spreading it all over the disk.