In reply to Aigen: I got this one:
http://www.montane.co.uk/range/accessories/extreme-mitt
It's basically pile pertex with a rubberised palm. The pile seems thicker and warmer than the buffalo mitts.
I have a pair of fairly thin* neoprene type gloves and thinies that I can get the mitts on over, but it turned out not to be necessary. I found that they are warm enough that it was more comfortable to whip the gloves off and put them in an inside pocket to warm up then wear the montanes against skin.
I was planning to wear them over buffalos if it got stupidly cold but at -12 or so it just wasn't a problem.