I would do what wr6133 said. The FX-4100 in theory can overclock to a higher frequency than the slighly older Phenom II 965, but a P II @4.0GHZ is going to have much more consistent performance than the FX-4100 at any frequency.
i can get a 955BE for $95 so i guess thats viable then
Comparing the 4100 to the 4300 Piledriver - seems the only diff is 200mhz on the clock and it only has half the L3 Cache. The rest is the same...Is that really worth it??
Well the 4300 PD isn't out yet, but that would be worth considering as a more viable replacement for the Phenom II.
Phenom II 955s are fine, really for the graphical limitations of a 6850, so is the FX-4100, but if the CPUs are all around the same price the Phenom II is going to be the better choice. Just make sure the 955 is C3 stepping 125watt TDP. There are a couple different variants of it. The C3 stepping is the final, perfected release. That can be checked by looking at the AMD model number on whatever site you're buying from.
"But the FX-4170 comes with a much higher 4.2 GHz base clock, and consequently offers compelling performance out-of-the-box. With a price tag recently lowered to $120"
As the FX 4100 is only 3.6GHz base and turbo core @3.8 GHz as compared to the 4.2 base and 4.3GHz turbo on the FX-4170.
Just a suggestion or you can wait and watch for the FX vishera CPUs
Also the 3870k APU requires the FM1 CPU socket and the other FX series requires the AM3+ socket so have you bought the motherboard already or you getting a buying decision on the platform, Personally I would recommend to go by the AM3+ route and get a Vishera CPU with better IPC and better clocks in a couple of months or so.