Well, I don't even know if it's possible to unlock cores on the regors...I know it's possible on the kumas and callistos (PII X2)...and on the hekas (PII X3)...
If you're talking about 400mhz overclock then yeah you probably will possibly see some improvement in gaming...
And Vista64 is only good if you have over 4 gigs of ram...
You should overclock this CPU and see what it gains in performance...
Also what graphics card do you have? you could overclock that as well...If you overclock both the CPU and the graphics card you could gain a decent amount of performance...My system got around 12K - 13K @stock and when I overclocked it I managed to get around 16K which is a surprisingly huge improvement in performance and score...
I will actually do some research to see if it's possible to unlock the regors...you got me interested...