For those with X48 based motherboards a nice discovery - depending on your motherboard it will support 16GB of ram, rather than the 8GB maximum advertised by board manufacturers and Intel.
After reading an article on another forum where someone put 16GB on an Asus P5Q I decided to try expanding mine. It does work. I have gone from 8GB of Corsair DHX to 16GB of Crucial BallistiX Elite without a hitch - plug and play. A nice bonus is that the Crucial memory also seems faster and more responsive. Timings are better too.
Corsair: 9-9-9-24-2T @1.8V
Crucial: 8-8-8-24-1T @1.5V
Motherboard is an Asus P5E64 WS Evolution
So for those (with Asus motherboards at least) it appears you can expand RAM past 8GB and breathe a bit of new life into your X48 machines. My VM's can now have some elbow room.
If anyone has the RAM and feels daring try for 32GB and let us know if it works!