To anybody with a new Samsung box that is interested.
I fitted a new Seagate ST3500830SCE 500GB drive today. I transferred all HD recordings and Anytime over using the excellent Copy+
and its now installed and running silently and without a hitch. No reboots, crashes or any other problems.
The drive has exactly the same power consumption specs as its small 300GB brother so I didn't expect any. The only small issue is that there are not that many of these drives about now being last years 'vintage'.
Overall though I'm happy with the result and glad I went for this drive.