I managed 11995 using my overclocked 2100+ (1845MHz) and slightly overclocking my Gainward 4600 (315 core / 685 memory). Can't quite break the 12000 barrier, but I think it's a cooling issue, and I'm not yet ready to make the jump to a watercooling setup or some other extreme variation. Besides, anything over 11k is great for me.
