I don't know what benchmark would give an unbiased comparison.

Build your own benchmark. Measure whatever you want to do. Or if you insist on standardized testing, use something like SPECInt 2006. Results here: http://www.spec.org/cpu2006/results/res2013q1/ (sadly no ARM results). Of course that is only for integer calculations, if you need fp, use SPECfp.

There's nothing that you can really condense down into a couple of simple numbers to use in marketing to non technical people.