I have an infinity amp, 2 10" perfect subs, and quite a few of gadget electronics hooked up and the 75 was fine. Check and see also the price difference. If a big one from the retailer you go through go with the 75 it will be fine, if not then step up to the 78. The biggest part of the 75-78 is the cold cranking amps, where almost all of us dont drive it in the winter or cold.