The answer to both questions (AFAIK) is no. I'm not an opponent of overclocking, I actually was one of the few folk overclocking with Lehto's1 early overclock kernel. You can do what you like with your device, I'm just giving you advice. Mines been stable and overclocked for 18+ months now, but then I'm not running NES emulators and the like either...

I still subscribe to the idea that one should be cautious about overclocking. We're talking about overclocking a chipset well beyond it's spec, in a device enclosure without much in the way of heat dissipation. Add in that the CPU is in very close proximity to other heat generating/sensitive sources (like the L-Ion battery), makes it concerning for me. Using a little common sense goes a long way here.

Just the fact that most can't go above 900Mhz and remain stable is a good sign that sustained run times at overclocked speeds (for tens of minutes or hours) is probably not the best idea. Short bursts, which is what you'll find in common usage, should be fine though. Your mileage may vary, based on your device and the environment it typically runs in.


1 For those who are "new" here: Lehto made the first set of overclocked kernels for the N900. Titan then joined in, improved on, setup, and maintained the kernel-power packages for a long time, followed by Pali who now is doing further improvements and maintenance. Kudos to all involved...