Valve spring pressure has just as much, if not more to do with stud flex as RPM.
If you're talking about running 130 Lbs of seat pressure, sure, you don't need a girdle.
If you're above and beyond that, a girdle is the only way to fly (unless you're using shaft rockers of course).
With just a mild solid tappet (non-roller) camshaft back in the early 90s, we started bending pushrods. We didn't have any clue as to why. The blower motor was being shifted at 6800 (a street car as well). We were recommended to put on a stud girdle (I think we were running about 160-170 lbs of seat pressure) and as such, did.
The bending of push rods stopped. After some more research in talking to guys faster than I, it was discovered that harmonics were causing the push rods to flex, and then bend.
Again, if you're not going to run shaft rockers, and this isn't a very close to stock motor, it's in your best interest to run a girdle.