[Motoman]

Basically, if you kept everything else constant (like motor,gearing,...), then more voltage means more motor rpms so faster speeds. More mah or capacity, means you have more disposable energy and so the vehicle will run longer on a single charge.

you need to find the right balance of both voltage and capacity that works best for your application. Consider size, weight, voltage, capacity, expected speed, expected runtime, brand, and price. Usually 1/8th scale buggies run great on 4s. A light setup in 4s would probably be around 4000 - 6000mah, but some people use bigger batteries like 8000mah. The 8000mah batteries are great but as I found out they are too big for an 1/8 scale buggy both size and weight.

hope that helps.