I haven't looked at the Supermags in a few years, but when they first came out,...I wasn't impressed. The insulation in the boot stopped at just below the ankle, so from there up to where the neoprene starts, it was just rubber boot. Not what you would call warm or a good design.
Does Hodgeman still offer the Dura Mags? Like I said, haven't looked at the Supermags in a long time, but the Duramags design was waaaaay better. They're all gonna leak, so one isn't any better than the other in that department.
I'm still running my Duramags now, and just yesterday I sealed ever seam on them with aquaseal because they've started leaking like the proverbial sieve.
I've hunted in some wicked ass cold weather in those Duramags and very seldom will I get cold. If my feet take on any kind of a chill, I'll get out and walk it off and it doesn't take long to build up heat in them.
I'm also a big proponent of heavy wool socks when it's cold. Silk works too, but I like wool. The best trick I can give you about socks is to find a pair that are absolutely HUGE and wear them over a regular wool sock. Stretch them out if you have to, put them in a vise and stretch the ever loving hell out of them! And then put them over your regular fitting wool socks. They gotta be loose to have the insulation factor. If your feet are bound up, they're gonna be cold.
If you have sweaty feet, spray them with anti-perspirant, let them dry, then sock up... Kansas may not have the reputation as other states for cold weather, but it gets damned cold here in the winter. Last winter was one of the coldest, for the longest we've had in a long time, and I worked outside almost every single day of it. We started one day this last winter and it was -12 and never got above 0 all day. And I'll guarantee there isn't much colder than standing in a snorkel basket on expanded metal.
My $.02 but it's worth about a dollar with today's economy.