Most uncut guys I've seen are bigger, but I think that's because you tend to see more natural black and latino guys that are uncut and they just tend to be bigger. I'm perfect evidence that just because you're uncut you don't necessarily have a bigger dick. You just don't see too many uncut caucasian americans.
Growing up I was the the only white guy in my high school that was uncut so I definitely felt self conscious, but I'm glad I'm uncut now.