Jock, it depends on your bow, degree of center cut, broadhead type, your shooting style, etc. I have no problem going from 125 to 160 most of the time, but some of my bows like a little stiffer arrow for the 160's. If I go to 190, a stiffer arrow is always necessary over the 125's.
I bare-shaft match with 125 field points (just because I have a bunch made up), then shoot my broadheads to see if I need to go higher in spine. If you can't see any difference between 125 and 160 in your broadhead arrows, don't worry about it.