It happened also with other updates so I always kept using 2.6.10/r... (don't remember), but now I wanted to try the new sources and I always get the same problem: the system is slower! Especially X11!

Could it be because of the high resolution console? I didn't pass any option at OpenFirmware level, but it starts at high resolution. Before it didn't.
Does anybody know if the problem could be related to some other misconfiguration of the kernel?

I don't find big differences with the old config...

EDIT:
The problem is more serious than I first thought since during processor-intensive works such as compiling, the MOUSE POINTER starts to flicker as if the system had no power left.
With the previous kernel I could do any sort of cycles consuming thing, but the mouse remained ok.