Unless you plan on running really RPMs getting that done to a crankshaft is kind of a waste of money as it doesn't really do much for power until the higher revs. My guess would be 10-15HP at 9000 RPM.

I hope that's not the only thing that's getting lightened in the rotating mass. Granted I doubt knife edging the crank really takes the weight down all that much, so it might be all right.

However, why spend money on something if you're just half-assing it anyway? There's better things to spend money on before resorting to knife edging the crank.