Wilde Racing is right.
Hypereutectic was created in order to have a tighter cold fit. the higher silicon levels allow it to expand less than a forged piston. Forged it just going to be stronger is all.

The only useful data i can find to reduce the slap is to rebuild the engine, bore it out some and try for a better fit.
But if it slaps with a stock bore, i don't see why it wouldn't with a larger bore.
Best i can put together from that is to have the engine properly balanced and make sure each piston and cylinder wall is as close to the same diameter as possible.

Thanks for the correction Wilde.

Trying a thicker oil might help, but I was always under the impression that these newer engines wouldn't lubricate as well on a thicker oil as the Gen 1's did. Any truth to that?