In winter I use LobsterClaw style gloves.
There are less seams so they don't leak as easily and are always warmer than 5 finger gloves.
The only negative is that ya can't give the finger to other road users.
Mine have a leather palm but a Cordura back so work really well with the heated grips.
I ride year round except when there is snow/ice on the roads so have ridden in -10C this winter just gone.
I was frozen solid after 1hr in the saddle but my fingers still moved and I didn't crash.
Even then I still couldn't set my Oxford HotGrips to maximum as they get much too hothothot!
Next time it gets that cold,.... I'm in the car!
The Rukka Lobsters are the best out there but $$$.
I use the ProBiker Lobsterclaws which are the best I can get in 4XL.
http://www.getgeared.co.uk/probiker_winter_gloves_coolbreaker4_wp_black?sc=16&category=146