It depends on the cam core. The bigger the core, the quicker you run into frequency issues. I learned it from Dan Jesel. So it happens more than you know. I sent him some Crane lifters I was killing. In fact, I called to order a set of his lifters that were a hundred bucks each back then in 1996. He wouldn't sell them to me,because he said I didn't need them. So I sent him a few of the killed piles of crap and HE made the diagnosis. He had me write a note to Chase Knight and I sent those lifters back and Crane sent me a set of Pro Series with .810 wheels and the issue stopped. Again, if you know anything of resonance frequency, you know a hundred factors can cause a problem. The diameter of the core, the materiel of the core, total lift, rocker ratio and even rocker materiel will affect resonance frequency among many more things. Again, the cheap ass lifter companies should not even make a .904 lifter with a .750 wheel. There is no reason other than 95% of the lifters they sell use that little wheel and they cost most less than the bigger wheel. Without spending a ton of time on a spintron, you never know what frequency you'll have issues with. And the consequences of resonance frequency are quick and devastating. We started with ductile rockers. 7100 would kill the wheel. It would also take the lobe off the cam, bend the pushrod, and bust the rocker. The next switch was to aluminum rockers and that took it to about 7500. Then 7/16 straight wall pushrods got to maybe 7700. And every time it killed a lobe, rocker and pushrod. Double taper pushrods got it to 7900. Then I called Jesel because it became apparent that the lifter went first, which was exactly what everyone else said wasn't happening. Live and learn. I've seen guys have issues at less than 7k. It all depends. Why risk it?