Yes but you will find that the higher mah pack will account for some of that. It is a trade off as higher mah packs will give you better average voltage over a run but they do weigh more. The C rating refers to discharge the higher the C rating the more power can be drawn from the battery. That being said most setups will not see much difference between a 30c and a 40c of the same mah. Paying the premiums you do for 40c batteries is really not worth it as you can pick up a good 30-35c pack for a lot less and the performance will be very similar to a 40c pack.