If you don't want to heavy overclock (only up to 805 MHz) and want a good battery-lifetime you schould install Kernel-Power 49 and Karams Battery-Patch. This will enable some good power-saving options and overclock your phone to 805Mhz. And you don't have to configure anything by yourself.
If you want some more: with KP49 it is possible to overclock N900 to 900MHz with power-saving vdd1 and vdd2 enabled. For overclocking up to 1150MHz vdd1-powersaving has to be disabled.