2GHz 6 core - what's the point?

At work, one of the test machines I work on uses two socket 2011 (6 core E5 2630L) processors. Which sounds great except each core is only 2GHz, so single threaded applications run slow.

Why are there even 6 core processors that only run at 2GHz? It would be badly beat by a humble 3GHz quad core in single threaded applications. In multi threaded applications, it would merely match the much cheaper 3GHz quad core.

Server usage, the whole reason those CPU's were created. Why is it on a test machine? No clue... Maybe a bit more insight to what its a test machine for would be helpful.

The test machines test network cards. The cards under test are connected to some in another test machine and scripts are used to generate traffic. The scripts are pretty much all single threaded (so a total of 3-4 threads when everything's running in parallel, one per card). I doubt the second processor ever sees much activity. (I'm thinking it was a machine that used to be used for compiling until they decided to replace it with something faster to make more effective use of the compiler licenses.)

But what's the advantage of 6 cores at 2GHz over 4 cores at 3GHz?