My mistake.
I was thinking dual cpu too but 395W it's a bit too much for a 2.6GHz, the dual X5675 use 300W at 3.3GHz.
The 2670 has a 3.3Ghz boost probably has a better IPC and has more cores. For crunching, the 2670 is going to get you more than the X5675. I would expect the two to be about the same clock for clock in single-threaded situations despite the slightly different clocks but, those extra cores is what's going to make it faster for crunching.
Read the rest of the review and I think you'll see that when those cores are used, the 2670s practically eats the X5680s alive and it takes overclocking over 4Ghz and doubling power consumption to get them on the same level.
Simply put, the 2670 is going to give you more for crunching than old tech is going to.
Example: