The answer, like so many "what is the best setup?" questions, depends on your specific workload.
- 2 x X7460@2.66 = 31.92GHz
- 2 x X5570@2.93 = 23.44GHz
Obviously, the hexcores are faster overall. However:
- Is your workload parallelizable? Maybe fewer, faster cores makes sense.
- Is your workload CPU-bound? Is it disk-bound? Memory-bound?
If you have a parallel, CPU-bound workload that accesses a smaller set of memory, I think the X7460s may be better.
However, you may find that the new Nehalem architecture gives you better performance on your particular workload (faster RAM & IO).
There is no right answer - it depends.
All other things being equal, I would recommend going with the Nehalem, as you can always upgrade to the hex-cores when Intel decides to release them :)