Here ya go. These results are for my boot drive, a WD Caviar SE16 WD6400AAKS 640GB HD.
The first graph is cache writing enabled. The second graph is cache writing disabled.
Note that the transfer rates are negatively affected when caching is off--more of the blue line is in lower territory. The maximum is the same, but the minimums and averages are different. The burst rate and access times are unaffected.
This is the result of one test only, but should be representative, at least of my drive. A hard drive engineer may well laugh at these tests and maybe correctly so--I don't know how much reliance to put on these results as they apply to the real world.