I'm pretty sure any gtx 460 will run 750 core without any other tweaks. The worst gf104 core i came across, out of ten tested cores, reached 800 before needing any more juice. They just beg to run faster, more like stock gtx 560 clocks.
And from experience, ppd scale almost linearly with clocks: from 725 to 910 mhz core means 25.5% faster. PPD came from 12k up to 15k (assuming 2387 or 5757 wu), 25% more points. The damned 5187 showed a more drastic increase: 8k to a little more than 11k, so a 38% ish addition.
If you can keep them cool, like below 70c, they will clock like there's no tomorrow.
My clocks were done under water, so don't expect more than 850-875 on air, but i like to see ocing while folding like turning a 5$ bill into a 10$ one!