I don't know if this is the right place for Custom Firmware releases but. I know moonlight stops by frequently enough. So let me get right to the point.
So I upgraded 1 of my 2 psp(s). 1 has 3.80 M33 and the other has 3.71 M33-4 and what I found was the latest Custom Firmware has slower read and write speeds. Using my application OpenBOR i found that the load times have increased significantly from lets say 20 seconds to almost 1 minute.
I performed a direct comparison between both PSP(s) with the same stick and those where my results.
Not sure if its Sony's fault or possible M33 issue?
{EDIT}
Ahhh, I just found this topic: here
Paraphrasing: Problems with MS should be reported to Sony, who has decreased the size of the fat Memory Stick driver from 185 to 95 KB (when decrypted), so they may have screwed something.
Perhaps you can restore if possible the 3.71 memory stick driver to 3.80 to gain that performance back? Hopefully they didn't change anything too drastic if it is possible!