Sliders are next on my list of things to toss money at. I think they are well worth the effort. The one issue I see is, from a stress standpoint drilling in to the Web or vertical surface of the frame has very little affect on strenth. However drilling in to the upper or lower horizontal surface has a great impact on the structural integrity of the frame.
As mentioned, get ones that you bolt on and don't worry. I have White Knuckles on my 4R, about the first mod i did on it. Cheap insurance after i bent up the rockers on my LC80.