If they leak take them back (or use neoprene or gortex liners)… You can test by putting them in a bucket of water or the bathtub…
If they are leaking cold snow melt to the inside your feet will be very cold..
if it's just sweat, my experience is that my feet are still warm… that's why they're sweating, they're warm…
Personally, it's hard to imagine having cold feet while snowshoeing at 40F as you wrote in your original post… snowshoeing is vigorous exercise and your feet should be sweating like pigs on a 100F day… of course, when you stop and stand around in snow for an extended time that's a different story… time for a dry socks change
as far as the rating goes you can throw that in the trash…
just like sleeping bag ratings…
everyone's circulation in their feet is a bit different… some will need warmer boots…
Further, if you have too much sock or tighten the laces or snowshoe bindings too tight you could limit the circulation in your feet… in that case it could be that no boot will keep your feet warm…
Billy