Our results here aren’t exactly conclusive—and they probably won’t ever be. AMD might be playing pleased about enthusiasts toying with disabled components, but most of its motherboard partners are being made to quietly plug that little…we’ll call it a little “slip.” Not that we blame AMD. Turning an X3 720 into an X4 920-equivalent costs the company $55. Unlocking 2MB of cache might keep an enthusiast from buying a Phenom II X4 920, costing AMD another $20 per CPU versus the price of an X4 810.

Of course, the more benign explanation would be that AMD is saving enthusiasts from instability when they coax a core or block of cache to life, and then it turns out to be flaky in day-to-day usage. Whatever the reason, though, platforms employing the old microcode are drying up as vendors update their BIOSes to include the latest fixes.

By and large, this seems much ado about nothing, though. Even among the vendors who’ve tested dozens of processors, there doesn’t seem to be a surefire way of sorting unlockable chips from those that aren’t. We were all over the place with steppings and production dates, as have the board makers to whom we’ve been talking.

Having spent money on retail CPUs and feeling the joy of getting that extra 2MB of L3, then the disappointment of not getting a fourth core, I feel fairly qualified in offering the following advice. If you already own a Phenom II X3 700- or Phenom II X4 800-series CPU, it’s certainly worth a shot to try unlocking them with a board that still supports this functionality (at the time of writing, ASRock’s M3A790GXH/128 still does). After all, you have nothing to lose by trying. Worst case scenario, you experience stability issues, turn ACC off, and continue on your way. But don’t go buying a Phenom II X3 720 because you read on a forum somewhere that someone else with a chip from the same production week got one and it worked. There’s a chance you’ll get a Phenom II X4 920 out of it. It’s more likely that you’ll get what you paid for, though—a Phenom II X3 720.  

Boards like ASRock’s are going to get increasingly difficult to find as vendors update their BIOSes to patch in the latest SB750 microcode. If you’re in the market for a new Socket AM3 Phenom II platform, then the 790GX-based M3A790GXH/128 is a good place to start—it held up well through hours of CPU and cache stress testing in Prime95 and Everest. There aren’t any 900-series X4s yet (though they’re on the way), so if you’re able to turn an X3 720 or X4 810 into an equivalent 900-series AM3-based processor without stability issues, more power to you. Just don’t expect it. And don’t be surprised if a future BIOS update reverses your unlock.

Given that all of the available Phenom IIs are separated by no more than $100, however, it makes the most sense to simply buy the processor you need. Perhaps it’d be a different story if we were turning a $200 Athlon into a $999 Athlon 64 FX of old. But for $30 or $40 bucks, I’d rather maintain my warranty coverage if I were planning to run at stock settings. And if you’re planning to overclock anyway, you’re likely better off getting an extra 100 or 200 MHz out of your triple-core chip, rather than unlocking a fourth core and hampering that overclock with a less-savory piece of silicon turned on.