Don't worry about the preload it won't be a problem. By hand they feel stiff but to get a better idea of how they will really feel then put a rail on a level floor and put slight pressure on with your foot and you'll see they slide easily. Be careful not to put too much force or they will shoot off with you.!!. . .Lol
In use they do free up a little but not massive amount and you don't want them to really. If aliagned and looked after correctly they will last for many many years giving hassle free usage.