Are you talking 360 or 318 pistons? The KBs tend to have the top ring closer to the crown so it gets a lot more heat hence the need for a larger gap. Hypereutectic alloys are lighter but more brittle and will fail faster than a typical cast or forged slug if you have detonation issues. The speed pros have the top ring land lower on the piston so the end gaps are less critical but you should still run a larger gap.
True, however I run speed pro hypers in my hemi six and at 180psi cranking PSI with an iron head i had detonation issues in top gear around 2500rpm for a good while and they handled it pretty damn well until I had it sorted out.
Pretty sure I have a spare 318 kb167 & a speed pro piston kicking around at home somewhere, when I'm back from overseas I can try to find them and post a pic showing the difference in top ring placement.