So a simple solution along DA's lines of thought; A CPU gets 50 credits from a project for crunching 24 hours (WuProp) regardless of speed or # of cores. A GPU gets 100 credits per 24 hours regardless of speed etc. Then all projects pay the same and everyone will crunch purely for the science.

Of course then all the folks with farms will take a look at their utility bills and wonder if it is worth it -or- there would be a run on Atom processors.