You need a kernel with h-e-n hostmode enabled. You need h-e-n GUI

You need a pile of spare N900, as OC will wear your CPU, no matter if hostmode or not.
Your CPU is like a car engine. It's designed to last 250.000km on normal driving. If you drive your car at limit all the time then european cars will only last 100.000km, US cars will explode after 100km :-P (here your N900 @ 600MHz(!) is like EU car). If you mix the fuel with nitromethane and go with RPM of engine way beyond what's been considered safe by manufacturer, then you may achieve exceptional speeds, but you know your car engine wears out and won't last very long. N900 CPU on OC will start to show sporadic errors, after weeks, or months of operation at actual CPU clock @OC, and it WILL NOT HEAL. A worn CPU is a worn CPU.

/j