1. A method of generating a distribution of performance ratios between multiple computer systems, the method comprising: for each computer system, obtaining results from multiple tests configured to test performance of the computer systems; for each of the multiple tests, calculating a ratio between the computer systems' test results; generating a histogram from the calculated ratios to indicate a distribution of the calculated ratios; and from the histogram, predicting the probability of an expected level of performance of one of the computer systems compared to another of the computer systems.