either will work for what you want, and everyyone will have their own opinion what to use. for me, if I can physically fit the gearing for the desired speed with a lower kv motor, then I use the lower kv motor. use the speed calculator and figujre what gearing you need to run for each to get your 70mph and then take a look at what you have, what you need to get what you want, and what will fit. most of all, have fun
