CFW 6.39ME (Minimum Edition) for OFW6.39 is a custom firmware for PSP by neur0n. It is supposed to work on PSP1000 and PSP2000 models. The degree of stability is still unknown.
Please test it on your own and refer to different people test reports.

Changes:

– Added a 166/83 CPU clock.

http://twitter.com/#!/neur0ner/status/106346123601510400