I have this doubt too. The differences between kernels released by sony, are more than we all see, right? I mean newer modules, maybe fixes for older hardware?
It's weird, I have a PSP BRITE 3000 now, but when I had a PSP2000 (Full CFW TA088-V2) and used 5.00m33 the battery life was extended by 2 hours aprox (meaning 4 to 5 hours of gameplay on default CPU clock, on brightness 2) while using 6.xx or higher would drain my battery in about 2.5 to 4 hours of gameplay. Would this behavior be related to resources being used, by either CFW and/or OFW?