Based on what I know. The chip in the N900 should run @ 550, with 600 being a default "overclock". Running 550 gives the device a lifetime of 10 years. 600 5 years, that's half the lifetime for a 50MHz increase (rough estimate). afaik these values are from TI (texas instruments) themselves. My rough estimes: 650MHz, 2.5 years, 700MHz 1.25... you can guess the rest I suppose. Also, according to joerg_rw, an engineer (not at Nokia mind you), damage to the CPU occurs due to http://en.wikipedia.org/wiki/Electromigration, not thermal factors. What annoys me though, is that apps like CPUFreqUI to report "raw" speeds, using a sensor that according to SpeedEvil, TI themselves suggest not using, and it's not on the CPU, it's next to the battery. Anyways, this is the info i've collected so far, what I said above is not from my personal findings (except my rough estimates).