"PreRunner" is a name that Sway-A-Way stuck on one of their lines of dampers, nothing more. Dampers are either all internal valving or a combo of internal and external valving ("by-pass"). By-pass dampers still have internal valving but it those are set really stiff so that the by-pass valving does all of the mid-stroke work.
2.5" vs. 3.0" would be determined by lots of factors; speed, vehicle weight, unsprung mass, application (pre-run, short course, or desert), etc.