I always appreciate caution, but unless Nokia got a special 3430 chipset that is "weaker" than the ones in the Archos 5 and Sammy / Motorola phones, 800mhz is well within the operational ceiling of the chipset.

The one caveat is if the cooling solution in the N900 is weaker than those units, but I notice zero temperature difference between 800mhz and 600mhz. I also have not noticed the battery to be draining any quicker, based on my normal use. I DO notice that the N900 performs very smoothly now, for everything to do with the phone. I could not say that before. The N900 is now just as smooth as the Droid (which is also at 800mhz max scale).

Kind of like (in a loose way) the SU7300 Intel chip. Stock is 1.3ghz, but ASUS and Dell both ship at 1.73ghz. I luv my M11X- almost as much as the N900

Hillbilly summary:

The N900 now performs smooth like I expected it too in November. My favorite apps (MAME and PSX4ALL) both play much better, as well as video and Flash content. So much so, I suggest the 600mhz is too weak for the design and function of the device (it is smooth now, but was not prior to OC).