The overall slowness on N900 is clearly a combination of factors:
The type of uSDcard in use.
The type of swap.
The time needed for Hildon to load properly.
The difficult 2 first boots.

The first boot from a fresh img is delicate. Be patient, and let Hildon loading for let's say 3 minutes. Then the first thing to do is checking if swap has been activated automatically or not. Htop shows swap usage.
Do not try to install anything or connect to internet without swap -and root partition extanded-
For example, apt-worker will start automatically if you connect your device to wifi.
Consequences: out of memory.
With precaution -using a fast uSDcard, extanded partition, swap- and after 2 reboots Chimaera is working well. Even better with overclock and the problematic 125Mhz frequency removed.