audioslain02. It is perfectly within code to use a larger wire size, code specifies a minimum size not max. Think about it, if for example you have a long cable run of 14-2 and, doing the math you find a higher voltage drop than acceptable you would leave the breaker as is and move up a cable size to reduce the voltage drop since larger cable means less resistance.
As far as folding the cable into a standard box, larger cable is stiffer, I wouldn't recommend pigtails, I'd install a larger box to allow more room to gently fold the cable tails in.
As far as folding the cable into a standard box, larger cable is stiffer, I wouldn't recommend pigtails, I'd install a larger box to allow more room to gently fold the cable tails in.