I went back to a 3.0GHz single core from a 3.0GHz dual-core. For some reason my games feel snappier. (Not to mention the whole system runs 10~20C cooler at any given time) Admittedly I keep my machine extremely clean (have a 2nd rig for dirty works) and while playing game there is nothing running behind. When I had a dual-core, even at same frequency with a single-core, games didn't feel that snappy. It's important to note the difference of being snappy and being free from occasional lags. Yah with a single-core, you'll get an occasional lag depends on what your OS wants to do while gaming, but other than that, I felt like my games were flying, which I could not feel with a dual-core.
This is such an irony to me because I've been a vocal supporter of dual-cores, but I can't explain it any other way. I'm also guessing the OS/drivers/applications, as well as the current dual-core architectures themselves, are not as efficient as it should be. A Recent review of Anand somewhat agreed to my hypothesis.
http://www.anandtech.com/cpuchipsets/showdoc.aspx?i=2736&p=9
At the same clock frequency, Opteron 144 is leading Opteron 165 in today's gaming. Time and time again I see results like this. Sure the opposite results are also abundant, but even a few example like this seem to convince me my own theory. (I mean, in an ideal world, dual-core should NEVER be slower than a same-frequency single-core) Also I noticed most video card benchmarks still ustilizes FX-57 (or an OC'ed equivalent) instead of dual-core processors on various websites.
Again, I believe it's imperative that you keep your system relatively clean to actually experience this. If I have everything I have installed in one system, dual-cores will be faster no matter what, for sure.