I re-flashed my second N900 (rootfs & eMMC) and then installed just rootsh + Compcache kernel-power.
It seems to work fine. Some lagging when ramzswap is full, but still responding quite OK.

Other N900, (KP+CSSU+speedpatch, etc...) started to lag heavily after ramzswap was full and eventually needed a reboot (or battery removal). I tried with speedpatch installed / removed, results was the same. Something is confiliction with compcache.

I'll add CSSU and other stuff to clean N900 and check what will happen.

EDIT: Installation steps (cumulative)
1) CSSU installed -> OK, no changes
2) Swappolube installed and "proposed values" applied -> NOK (stop responding, battery removal needed)
3) Swappolube and just swappiness adjusted to 30 -> OK (better that proposed values, but lots of lagging when heavily loaded)
- Annoying lagginess starts somewhere when +50M flash swap is in use. Below that it is quite usable.
4) Speedpatch (speedpatch_0.4.deb) -> Best performance so far. Ramzswap full & +70M flash swap and device is very usable and lagging is very minimal ( I had to test this even agreed to keep it in separate topic)

EDIT_2:Copied same settings for the other N900.

EDIT_3:With the other N900 problems started again after some usage. Load averages are showing: ~10, ~8 and ~3, but there is no program using CPU more that 2% and CPU freq is at min (min = 500MHz, max=805MHz). This ghost loading is causing lack of responsiveness. Any ideas how to find out what is causing extremely high constant loading? Top and Conky are not giving any additional usable information.