They still sell Phenom 1 9950s on Newegg, lol. I'll try to do a little summary thing here:
Phenom II X# ###
The first # following the X is the number of cores it has. There are the following:
2 cores: Phenom II X2, can be unlocked into 3 or 4-cores since to meet demand, working chips are disabled and can be re-enabled
3 cores: Phenom II X3, can be unlocked into 4-cores
4 cores: Phenom II X4, if it is a low-end 8**, the missing cache can be unlocked to turn it into a 9** proper quad. The 960T however, and any new quad that will have a "T" following the 3 digit model number, is a crippled 6-core and can unlock to a full 6-core.
6 cores: Phenom II X6, the big cheese. 6 mother****ing cores.
The following 3 ###s are the model number. The first number almost corresponds to the number of cores. I say almost because of one exception:
All 2-cores are 5, so for example, Phenom II X2 550 or 555.
All 3-cores are 7, so for example, Phenom II X3 720 or 710.
Low-end 4-cores are 8 and high-end 4-cores are 9.
Phenom II X4 810 is a low-end 4-core that is missing some cache. This cache can be unlocked to turn it into a 910.
The second two numbers are a bit more random. For example, the highest end triple core is a 720 whereas the highest end quad core is a 965.
Phenom II CPUs to avoid:
Phenom II X4 920, 940 - these are AM2 chips and can only work with AM2 DDR2 motherboards. They are fully fledged quads but they are not AM3. However, all AM2 boards can accept AM3 processors because AM3 processors can work with both DDR2 and DDR3
Steppings:
The older stepping is the C2. C2s have ****ty IMCs (integrated memory controllers) and did not overclock very well. The CPU itself was fine but to gain overall system stability, sacrifices had to be made. My CPU is like that. The CPU itself can do 3.9GHz at 1.5V Prime95 Small-FFT stable (Small-FFT is CPU-only). The memory passes memtest at 6-5-6-17 timings, 1333MHz (which means it should work fine). However, to pass Prime95 Blend, which stresses your RAM and CPU and motherboard, I have to run my 720 at 3.7GHz with 1.55V and my memory at 7-8-7-22 timings because of the weak IMC.
The newer one is a C3. Some chips are guaranteed C3s. Phenom II X4 965s are C3s as are Phenom II X2 555s. The Phenom II X2 550 has two versions. The C3 with a locked multiplier (so, not a black edition), or a C2 with an unlocked multiplier (which used to be the flagship dual core until the 555). The only X4 955 left on Newegg is a C3.
Hope this helps.
Take all unlocking information with a grain of salt. I'm an unlock advocate but my 720 cannot boot unlocked. My sister's 720 can boot but is not stable enough to run the Start Menu, so the 4th core is truly unstable.
