Rab Vapour Barrier socks

Cross post from gear discussion, figured might get more info here. 

Does anyone have any experience with these? Sounds like they work phenomenally from the limited feedback I have heard. Does anyone have any input on sizing? 

Medium - US Mens 8-9, EU 40.5-42

Large - US Mens 10-11, EU 43-44.5

I am typically a 9.5 street shoe and my G5's are a 43, so I feel like I am right on the edge of a medium or a large. May wind up just ordering both and returning, but if anyone has any experience with them sizing small or large could be helpful. Any other alternatives I should be aware of? I often use produce bags for impromptu versions of these but got an extended single boot trip in the works and I feel like I will be happy to have the real thing. 

Thanks!

Rab Vapor Barrier Sock

Had similar 35 years old made by Chouinard. They are a sack that looks like a sock. Such sacks get folds in them, which at first are not bothersome. But after sometime the folds become bothersome.

Get a neoprene sock they work much better and cost 25% less.

I tried them out a bunch a few seasons ago, as far as sizing I can say that I'm a 8.5/9 M in US and wear a 41.5 in my Nepals. I got mediums and they fit well but I'm close to the max end of its range. I'd go for the large if I were you.

What other type of feedback were you looking for? I initially got them because I read that they could add some warmth to my single boots which weren't really cutting it for most of the season for me. I didn't feel that they made a noticeable difference in keeping my feet warm, and now use electric socks which were more costly but much more effective. Occasionally I will still use them for overnights to keep my socks from absorbing moisture which is their main purpose anyways, they're very good at doing that.