Totally see how it hangs over the knees though? I have a feeling double fabric would not do that. But my guess is as good as anyone else's.
Ditto on anyone's guess, but I think if the double was cut right, judging from the small test you did with the double-lamination that you posted the pictures of above, it could do that too. It seems like it has enough bulk that it could potentially behave almost like the neoprene in terms of bulging just a little at the knees. You can also "fake" some extra stiffness at the knees and elbows with thin interfacing if you needed it, to take out some of the stretch if it was TOO tight and fit more like the lycra.
Darn on the sample size, but I'll get over it.

Will just have to wait for my actual fabric to get here to start sewing, I guess.
As for the fact that nobody on the first run was experienced with the fabric... I'm not either. *giggle* I've never sewn neoprene, or anything that thick, in my life. I live in landlocked Ohio, so surf shops are few and far between, meaning people who can make surf wear are also few and far between. So I'm kinda on my own here. It'll be an adventure.
Benkenove, I'm not sure I understand what you mean by "finish," but if it's as I understand it, the texture or shine of the fabric, both are going to be the same, as it would be the same lycra over top of both the double-layer nylon and the tricot neoprene. It'll look the same on the outside, it'll just be thicker and less stretchy with the neoprene.
I know you're all about accuracy, and I would never try to talk you out of that (because I LOVE when people are that concerned with everything being "right" so their costumes always look amazing), but I do also think that the neoprene that we can get is NOT as accurate as we would like it to be (ZIA's post about the LFL budget above neatly sums it all up), and pattern drafting is only going to account for a certain amount of the bagginess we're seeing. I think the lycra backed with nylon only is going to behave more like thin neoprene than the tricot that actually contains the thin neoprene, just because of bulk and lack of stretch. Again, the pictures posted above give you a good idea of the way the double fabric will roll at the elbows and knees, like the real suit (we hope). It's going to move more like the very thin wetsuits that you use for warm-water sports, not the tricot that's approaching the thickness of cold-water gear once it's all layered on there.
http://www.wisegeek.com/what-is-neoprene-rubber.htm has a nice writeup on neoprene as a material, and it mentions suits that go from .5mm up to 7 mm. Thickness on the tricot is 1.5-2 mm, according to ZIA, so it's up there in size after everything's piled on, even though it started as thin as we could get.
Again, not arguing with your desire for accuracy at all, just trying to explain that at least from what we know so far, the double-lamination might BE just as accurate as the tricot, depending on how it stitches up, and we don't know that yet.
:cheers
Julie