Ok, scratch my previous post. I was wrong.. or at least I wasn't testing properly.
I was adding options in /etc/modprobe.d/options like 'options nvidia ..'. But it seems in ubuntu this doesn't work. They use some weird scripts because of nvidia_old, nvidia and nvidia_new what I just did was the following:
modprobe --ignore-install nvidia_new NVreg_Mobile=1 NVreg_RegistryDwords="PerfLevelSrc=0x2222"
and then, to check that the parameters were actually processed:
zapek@bacterion:~$ cat /proc/driver/nvidia/registry | grep Mobile
Now I'll let the system run for a few days to see if it fixes it. If so I'll try to investigate why the parameters aren't passed if one uses /etc/modprobe.d/options (I'm pretty sure they are for other drivers though).
BTW, NVreg_SoftEDIDs=0 doesn't seem to work for the latest driver, it tells that the parameter is wrong.