Ok, that was kind of an obvious answer, but there are truly a myriad of variables to consider. I actually get this question pretty frequently. For current Intel server products, if everything else is equal you might get slightly better performance with two 2-core processors.
I checked for a good level comparison, but couldn’t find the ideal combination of plaforms, and configurations.
Looking at TPC.org for TPCC results I found the following:
1 socket, 4 core, 5355 based system scored 145K
2 socket, 2 core, 5160 based system scored 169K
i.e. 2 socket solution was only about 16% better
You will need to look at what is your best solution for now and future.
With a move to integrated memory controllers in the next generation processor, a single processor will reduce the number of memory slots available, and therefore change the calculation.