Trust me, it's not slower clock for clock.
Every time you run a 3D bench, even at the same settings, it may be a little different. Do a given bench at some given settings. Then reboot and do it again with same settings and everything. You very well may get different numbers
For even more score variation, reinstall windows, flash a different BIOS, or anything else like that
Run SuperPi and your numbers should match up a little better
Believe me, I have ran this test a hundred times, and the results are very consistent. The 8600 is always 400 points behind the 8500 in vantage, clock for clock. It's only when I give the 8600 a 400mhz boost that it can tie the 8500 (and this is because of the CPU score..the FPS stay 1 frame behind). Now in superPi, here are my latest results to compare: (8500 results were recorded yesterday before new CPU istalled)
Windows XP
e8500 (9.5x422) 1M 11.6sec
e8600 (9.5x422) 1M 11.6sec
e8600 (10x440) 1M 10.6sec
Vista (This is a real pain waiting for this program NOT to crash in Vista...)
e8500 (9.5x422) 1M 11.70sec
e8600 (9.5x422) 1M 11.79sec
e8600 (10x440) 1M 10.79sec
Now this looks promising, (except for the 10th sec difference in Vista) but the Vantage scores are consistently behind..same exact hardware, fresh windows install, same source drivers and same clocks.
Something else weird, but worth mentioning..in checking for stability to get up to 4.42ghz, prime95 never failed, throughout the gazillion different settings attempted....the computer bluscreened and dumped it's memory load, and restarted....but no failed prime runs like I am accustomed to.
That's really not important, just weird. Now that I am Prime stable for 12 hours, this was the clock I was going to stay with. I say "was", but if I am going to get worse graphic benchies, I would almost rather keep the 8500. I am tempted to put the chip back in, but then I would hose my DRM for the second time in two days