I usually gage the cpu performance by running super pi (I run a windows VM in Parallels Desktop). For instance, an early mbp 17" I7 2.2 ghz run the 2million decimals calculation in 28s. The latest version of mbp rd 15 I7 2.8ghz run the same calculation in 22s. If you cannot run it take a look here: http://browser.primatelabs.com/mac-benchmarks. Find both models and compares the scores. For my old and new models it showed an improvement of 30%, however, as you can see the result from super pi, the improvement is 21%.