Just read the piece on Wetsuit technology on Slowtwitch. The underlining take-away from that article was the importance of 5mm rubber on the legs.

Looking forward to part II of this article and hoping there is some talk about the 2 peice Desoto suit and its performance when only wearing the lower portion.

I've done my own testing using only the lower portion of that suit and found it nearly as fast as wearing both the top and bottom. But, my tests are very informal and really consist of just going all-out for several sets of 100's with and without the top.

But, I think the article is accurate in that there needs to be max rubber on the legs to make a wet suit fast.