The official rPerf rating (relative performance rating of Power based machines) are available in the pSeries, System p and now Power Systems "Facts and Features" documents that are on the IBM website. It is best to use Google for them (searching for "pseries Facts and Features" works for me).
You may want to know the rPerf rating for your LPAR and an LPAR that is not one of the officially rated numbers of CPUs/Cores. There may be ratings for 8 and 16 CPUs but your LPAR has 13 CPUs! Well, you can run the rperf script on the LPAR and it will find out the model and count the CPUs, determine the nearest rPerf number and then does a simple linear calculation to tell you roughly the rPerf rating. This is not a IBM blessed function but a freely downloadable shell script and simple enough to update. This can be useful when considering consolidation of workloads to newer machines and deciding the LPAR sizes or comparing LPARs that are on different generations or types of machine.
Find script at