Do not get the largest bag available, especially if you are buying a roller bag.
I had a buddy that was riding a 155 board, and bought a bag that was probably in the 180 range. The board is what keeps the bag stiff, so when he was wheeling around his bag, it looked like a giant limp dick.. he hated it. It was also a pain in the ass to transport in the car since it was about a foot longer than all of our other board bags.
He ended up buying a Burton Wheelie Gig bag in, I think, a 157. He can fit a ton of gear in there, and he maxes that bag out at 50 lbs; the weight limit for almost all the airlines.
No need to worry about the large binding either...
Nobody likes to carry around a limp dick.