The
E5-2651 v2 is based on
Ivy Bridge architecture while the
E5645 is based on
Westmere.
Using the multithread performance as a reference, the E5-2651 v2 gets a score of
415 k points while the E5645 gets
77 k points.
Summarizing, the
E5-2651 v2 is
5.4 times faster than the
E5645 . To get a proper comparison between both models, take a look to the data shown below.