I think that this question might be better asked to the folks who frequent the "Reloading" forum here. I don't reload, but I am a chemist, and it seems like there's a really big difference between 150 and 100 grains of powder in a load, but I can't be totally sure...
Everyday experience, in that case, generally tells me that if you're changing something, change it less drastically and things will work better.

Nate