I have 2 phenom II 965BEs ,a 1090T and just got a 960T. I asked this question long ago when i went from my first AMD x3 720 on an Asus M4A790 EVO XTD. it amazed me as it changed to the 4core immediately upon boot..
I asked about the next 4cores as soon as the thuban came out, thinking of the 720 experience. I got the same types of answers as posted here.
I had no luck with the 960T on the same Asus 790 board. just would not post or blue screened if i had the core unlock option. It works very well as the 4core though and overclocks at very low volt increases. I started high and kept backing down. I began at 1.4750 and got all the way back to 1.3125 and boots no problem now.
I find my 4core 965be i have at 3.8 with the multiplier bumped up and only minimal fsb increases , to 220, has run steadily and constantly for a year at that speed no issues. i put a 128G crucial m4 and now get instantaneous response from everything from iTunes to Netflix via WMC. no wait. The 1090T is no faster and i have it up to 4.2G only it runs hotter as ambient temp goes up, the proportion of difference from ambient to load grows in a disproportionately higher level than the 965be doing the same thing in the same room. I get that type of response from the 960T. each is cooled with air only , CM 212 Hyper plus and Xig.1284ee or 1283s and all coolers use push/pull higher speed fans on controllers delta 3k panaflo and Scythe slipstream and ultrakaze3k. all of these set ups keep the cpu temps well within acceptable temps. idle temps are in the under 90ºF and only the 1090T @4.2Gs will hit 126ºF on full load 100% over 20mins and over 72ºF room temp(74-77º)
So,all my stock cores seem to operate quite well , 2never could be overclocked and stayed 4,one was already 6core and the fourth one never made the OC was only 4core , not 2 lurking waiting to be unleashed. My only success in core unlocking ,the 3core 720BE, worked in 4core and kept very cool, only ,it was just fine and appeared as fast in 3core mode. so i kept it at 3. it ran a few degrees cooler and i could overclock the 3cores any way. all i needed back then .