What are your waist sizes? This is how I size our bibshorts
2X is 38" to 40"
3X is 40" to 42"
4X is 42" to 44"
4X is the largest we make them in.
One of the challenges in making 3x and 4x is that there is a much bigger variation in body shape among guys with 42" waists than guys with 32" waists. In other words there might be a guy with a 42" waist with who has an athletic build and another guy with a 42" waist with skinny legs, no butt and small chest-totally different builds.
On nice thing about bibs is the waist size is a bit more forgiving than with regular shorts because bibs don't have elastic at the waist.
Dan