Yeah.. a reflash would probably solve your problem. If it's not a harware fault. Do not trust the temp as it is not exactly. It could have been hotter. You might have fried the recievers of the n900 while running at that speed (hopefully not). They are probably more fragile. Have you tried the GPS?

If the keyboard feels warm i would rekommend running att lower mhz. Even if it not stops working at once it will tear on the hw and eventuallt "dry" it out.

Please let us know how it goes. You must be the first one this close to fry the device.