The bus runs at 33MHz in both the Q950 and the Q800, doesn't it? Where the 800 beats the 950 is in having faster and more readily upgraded ram.
I recently acquired a very nice 800 also, and like my 840av and its younger siblings, the 8100, 8500 and 9500, it is by nature a quiet machine (unlike, say, a Q630 and its siblings, in which the PS fan is annoyingly loud). This leads me to think that your vibrations must be due to a defective hard drive that could do with replacement. Alternatively, you might do well simply to check the drive sled screws in the first instance.