Socket 939 3700+ was 2.2GHz. Your FX 57 was the fastest chip made for 939 but the problem was/is that it is only a single core.
Not true. Either by overall speed or clock speed.
The FX-60, a dual core 2.6 GHZ processor was faster overall as was its opteron 185 counterpart. There appears to have been an opteron 190 dual core at 2.8 ghz. The socket 939 opteron 156 was a single core that ran at 3.0 GHZ was the fastest clocked part on the socket.