It really is a matter of choice. Try 1/4 first and see if it is noisy. Generally I use 1/2 with aluminum heads since they grow more. I don't think the lifters pumping up is too much of an issue any more, I think it is the lifters compressing that is the power robber. I run the Morel lifters on my hydraulic roller and I have them at 1/2 turn. It runs to over 6000 llike that with .535/.550 lift. But now, after replacing the studs, WATCH IT CAREFULLY!!!!! Like was said, preload is not the issue. If it is still coming loose after everything I said to do, then the cam is wearing or the lifters are just shot. Because regardless of preload, as long as you set some, the pushrod should NOT have lash in it.