Buoyancy is buoyancy, no matter where it is located. All things being equal, and that the different 'balance' of a long john doesn't 'fix' a problem with your stroke, a full suit will be faster. This also assumes that the arms on a full suit doesn't restrict your stroke.

I have yet to find a full suit that doesn't restrict my arms in some way. Grew up surfing so I've tried a lot of wetsuits in my life. I primarily use a long john because it doesn't restrict my arms.

How much time do you think a full suit can make?

I've got both a full and sleeveless Aquaman Bionik. They both fit well. I feel the full is faster but not by much.

I have found that while swimming through surf, I get a lot of water in my sleeveless.

jaretj

That's a really hard question to answer. A lot depends on your proficiency in the water, your stroke, your kick.

Overall, I'd say the differences are small, so I wouldn't sacrifice too much comfort for it.

I have a swimming background, and swam in a a sleeveless for many years before switching to a DeSoto T1. I felt more comfortable in the sleeveless at first, and likes having the 'feel' for the water. I really like my T1 now, and feel I am faster.

Dan's got an article here somewhere about this issue - worth looking for. He is pretty emphatic about using a fullsuit - that it is the fastest, plain and simple - and that it will save you both time and energy because fo the extra flotation in the upper body (and the fact that your arm is wider, so you pull more water).