Don,

My understanding of the 1/4 vs 1/2 vs 3/4 power difference is as follows. We are talking about a hydraulic lifter that has a cavity that fills with oil to allow for expansion and contraction in the valve train due to variences in temperature. In a solid lifter valve train this variation id dealt with by a small clearance, usually .014-.030, adjusted between the rocker arm and valve tip. Back to the hydraulics, The cap inside the lifeter has a range of movement inside the lifter and that is what you are adjusting. The less you tighten the hydraulic lifter the more oil will be allowed into the cavity there by making the lifter a little taller and increasing net lift to the valve. It's a very little difference that could be made up for by changing the cam grind if you were starting from scratch. The downside is you take some of the hydraulic adjustment range out of the combination. That's pretty simplistic but that's how I understand it.

Pat