Yeah, I too was forever "stuck" on 3.90 M33-3 as I thought the MS Driver only worked up to 3.90. I read on a link from DAX forums somewhere that (after struggling, it was a Spanish Post...) you could use the 3.80/3.90 fatmsmod.prx installer for 4.01 M33-2 as long as your 3.71 fatmsmod.prx file was unencrypted and not sigchecked...I didn't know about the 4.01 port of fatmsmod, that would have been big news and I might have upgraded if I did. I usually don't trust installing things on my PSP if I don't see it talked about openly on news sites/forums. Did it work for you?
...I (and another guy I chatted to on DAX forum) tried this 4.01 approach on 5.00 M33 (it takes two passes of the installer to get it to "work"), but afterwards there was no difference - i.e. the lag remained.
Apparently this is because Sony have changed the file, it's no longer called fatmsmod.prx, it's now simply "fatms.prx", though it was noted by some of the more knowledgable people over on the DAX forum that it wasn't simply a change of filename, it was a different file / driver entirely...
Either way, it looks like if you want the iso performance of 3.71 the highest you can go to for now is 4.01 M33-2 and apply the patch with a dump of an unencrypted (and not sigchecked) 3.71 fatmsmod.prx...
Though I must stress I've not personally tried this on 4.01 M33-2, but applying it to 5.00 M33 didn't brick so...
Let's just see if DAX doesn't bring out a 5.00 M33 patch, maybe because the patch "works" in 4.01 M33 was why he never brought out an "official" 4.01 M33 version...
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