I'll put up one Bitcoin in bounty for a CPU-miner (standalone) that will run on both windows and linux and outperform the built-in miner.
How much does it need to outperform it?
I'm looking into possibly adding support to BFGMiner.
since primespersec doesn't seem to have comparable meaning, it would be difficult to compare performance. Maybe primespersec could be normalized to the size of the primes and to the length of the chain?