in reply to Wasting time thinking about wasted time
One way to help mitigate this is to test on a network filesystem with attribute caching disabled (e.g. many NFSs use the -noac option on the mount). You will probably still see server side caching effects, though I imagine the network delays will tend to dominate.
Another way to handle this might be to put the results for file attributes into a hash before the actual benchmark timing, and then introduce a constant delay during each lookup. (You could time how long it took to fill the initial hash and then use that to compute the delay, but then again this too can be affected by a warm cache...)