Of the several springovers I have seen and driven...none were mine....they drove as much speed as you wanted to push them to...had one over 70 for sure...Thanks Drew!!...and they all handled fine. It would apear that running higher than 39.5 inch tires would require body lift or additional spring lift as 39.5 clear, barely, at full articulation. None of these trucks seemed to suffer from limitations in travel front or rear...they had 2 leaves removed on each corner and the ride and flex was incredible compared to the stock truck..that with v-8 power, even an average 350, will turn a stock truck into a completely different vehicle....you wont ever go back...
I think wheter you go 4 speed or auto is personal preference and would depend on what ratios you are looking for on the low end and the high end, possible overdrive, and if you would rather have a clutch or not...that part could be very effective either way.
brute4c