I asked the same question a couple of weeks ago at a Cruiser club meeting. The price difference locally was only $2. Everyone suggested going with the 60", which I did. That sucker is huge and in retrospect I think the 48" may have been adequate for a 2.5" lifted truck with 33's, but what's done is done. Consider your lift and tire size before deciding.
Get the 60", you will be happy you did when you get stuck off camber or in a weird spot. I like the 48" and own one of them as well, however the 40 seems to need the 60" more often then not.
A 48 is pretty worthless if your truck has much lift or if the terrain is soft. remember.... this jack is for extractions... it is a poor choice for tire changes and rhatr rype f use... carry a screw or bottle jack to use under the axle for holding the rig off the ground for repairs...