Described embodiments provide storage system evaluation and comparison processes. An aspect includes sampling data points for a workload running on system over a sampling period. The data points indicate a performance metric with respect to operational characteristics of the system. An aspect further includes subtracting a system specification value from each of the averaged sampled data points, thereby producing deviation values reflecting a deviation of the sampled data points from the system specification value. An aspect also includes averaging the sampled data points, calculating a standard deviation of the averaged sampled data points, and dividing the variance value by the standard deviation, thereby producing a modified performance value that accounts for a deviation in the operational characteristics of the system over the sampling period.