Which mining software/script provides the greatest MHash/sec and power efficiency balance? Hopefully this is not too specific..

Which mining software/script provides the greatest MHash/sec and power efficiency balance? (I'm currently using an old version of phoenix miner)

Preferably for the 5xxx series of cards, but if some mining programs are generally more efficient than others in terms of MHash/sec to power usage ratio, those are also welcome.

Thanks
My experience with a 6990 rig is that m0mchil’s Python OpenCL GPU miner is the most efficient one for me.

But I would try them out on a 12 hour basis, and do a comparison. Maximum output might be very different between software/hardware combos. Would love to see the results.