Slower per-core, certainly. But for some workloads more cores is worth it.

I should have been more specific. They're so much slower per thread that they're still slower overall even in heavily multithreaded tasks.

In this Anandtech review, the 16 core Opteron trades blows with a six core Xeon (clocked at 2.3ghz vs 2.66ghz):

http://www.anandtech.com/show/5058/amds-opteron-interlagos-6...

The 8 core DP Xeons weren't out yet when that review took place, but the Sandy Bridge chip was a big improvement over Westmere, in addition to the extra cores.

I'm not sure it's such a slam dunk -- a brief scan of the virtual machine benchmark didn't seem to have a more heavily concurrent load. Plus the Opterons are substantially cheaper.

If I was building a server I'd probably look at the Intel parts, the cost/performance curve is justifiable. But my personal case right now is running lots of test VMs simultaneously on a workstation, the Opterons are more attractive.

I should probably have linked to Sandy Bridge EP vs Bulldozer, which is much more lopsided. The 6C holds its own nearly everywhere, with comparable price and much lower power usage, and there's always the option of bumping up to 8C when needed:

http://www.anandtech.com/show/5553/the-xeon-e52600-dual-sand...

This latest generation was not favourable for AMD. 16 core Interlagos in many cases barely outperforms the old 12 core Magny Cours.