Neoseeker has published a brief report which attempts to look at the gaming performance differences between a highly clocked Dual Core Pentium D versus an equivalent single core Pentium. We took an 840D and 670 and push both to 4Ghz, then compare their performance in several current day games on single and SLI 7800GTX cards.
"Remember that with a single card, plunking down a second core into the system did absolutely nothing. With SLI, there are clear performance improvements at the lower resolutions where we still manage to avoid hitting the video cards' limits. Once we get down into the very high resolutions, the dual core advantage is diminished to nothing, because the balance of power transitions over from the CPU back to the 7800s."