An idea would be to use: YEAFFT and Glucas which can calculate primes using Lucas-Lehemer tests.
It does support x86 macros but it can also be compiled for other platforms using pure C.
I could compile it for the N900 and see how it would perform.
If it works and the selftests are a reliable way to determine stability, then I would need some info regarding setting kernel frequencies/voltages and some tips on howto boot the n900 in read-only mode.

An idea would to compile titan's kernel with the filesystem embedded in the initramfs with just busybox, the tools to set voltage/frequency and gllucas to determine wetter we have a stable frequency/voltage combination.

Then after the tests are finished we clock to a stable freq/voltage, mount the internal memory partition, and copy the results so we can set up kernel-power and power.conf for nitdroid.