You should know that not all CPUs with disabled cores will be stable when the hidden core(s) are enabled. You can find a plethora of information on the gamble of unlocking cores and why they're hidden to begin with, simply by searching the W³. The "10 peso version" (Three Amigos movie reference) is that when AMD creates X4 chips, some of the cores don't pass their internal quality checks and are then disabled. These chips with disabled cores are then branded, packaged, and sold accordingly.
Should you opt to buy the X3 you should know there are a few caveats that go with the extra core:
1. The BIOS, CPU-Z, and the OS often see the CPU as a Phenom with a non-standard model number and without L3 cache, which is what you're reporting.
2. The on-die core temp sensor will no longer work. You'll still get a CPU temp in BIOS and in software programs, which is the motherboard CPU reading, but you won't get a core temp anymore - or if you do it will be some outrageous temperature.
3. The fourth core may give you some instability. Most X3s will run as an X4 at stock speeds, but may need more core voltage (vcore), and they may not overclock as well, though that's not always the case.