Did you read the Wiki documentation for Overclocking? Nokia does not try to make the N900 work well with overclocking. Different N900s are different with regard to overclocking. All Nokia tries to do is make sure the N900 works at the speed they delivered it to you. This doesn't mean the phone you got is "lower quality" in general than any other N900. You should be happy your N900 overclocks at 850. That isn't guaranteed either. I overclock mine to 850 and have never tried higher. 850 is a good safe setting for most people.