might be limited due to i/o speeds or upstart version lacking some optimization. if an initrd is used it tends to slow it down a bit. can't tell at the moment, rather worryingly /boot appears to be empty, despite kp and k listing files installed there.

my eee 1000 with standard ssd's and a 2gb ram upgrade will easily go from grub to lightdm login screen in 4.8s according to systemd's analyize app. with a slower processor, less ram and probably slower flash memory, i imagine n900 with tuning will still be more than 8.

if it's something your interested in looking into, start another thread as it's a bit off topic here.