Intel Core i7 2920XM is the fastest sandy bridge notebook processor till date. It has XM suffix to it and thus sports Extreme edition branding. It has 4 cores and can handle 8 threads at a time. The Core i7 2920XM runs at 2.5GHz which auto-overclocks itself to 3.5GHz under Turbo Boost mode.
The Core i7 2920XM has unlocked multiplicator which means it is easy to overclock. It also supports HyperThreading, AVX, Quick Sync, Virtualization, including VT-x, VT-d hardware virtualization. TDP of this extreme processor is 55W which is pretty high for a notebook processor but since it is being used in gaming notebooks like Alienware M18x, battery life should not be the first thing on your mind. Check out the performance of fastest Ivy Bridge processor, the Core i7 3940XM.
The above chart shows how fast the 2920XM is compared to the Core i7 2820QM, 2630QM and 2620QM. 2920XM scored 18908, higher than 2820QM and of course 3 times as 2620QM.