jp3 best on truggy gives alot of bottom end and good mid to top.
if you are running buggy would run jp4 has a little less bottom and alot of mi to top alot
as for vspec when running that you should only use os 2050 pipe if want the full potential of the runtime and smooth power jp3 works with it but in a buggy it has way to much bottom end for a mid sized track will be all over the place out of turns jp4 would be better but os 2050 the best for vspec