Are you trying to ask how much performance you're giving up if you run 1.5s instead of 1.6s?

The only way to KNOW costs time & $$$.

My OPINION, based on some rocker ratio testing I've done on less "serious" combinations, is somewhere between zero up to maybe 10 HP, and that's only if the combination is under-cammed. I don't think it is, which is why I wouldn't expect it to make much difference.

With a .690"-lift cam, you could also be right on the edge of using a spring that can handle the lift w/ 1.5s, but can't cover the additional lift of 1.6s. My PAC 1243 springs with a 1.90" installed height are good right up to .700", but trying to go with more lift would require a different spring that requires a taller installed height, too.