I use the oxford grips and combined with some handguards and intermediate gloves commuted 1 hr on the motorway each way last winter. Temperatures went down to -4 without the windchill. If it went any colder I'd have to consider consider heated gloves or the muffs. The windchill is the real killer at those speeds though.

Also worth pointing out is that with that combo that summer gloves don't give enough insulation against the wind on the top of your hand and winter gloves insulate your hand from the heat in the grips to much wheras intermediates seem to strike a reasonable balance. For waterproofness for the length of journeys I do both my gore-tex gloves seem to do the job nicely at keeping the water out but then my cheapest gloves are �80 (a Bikers pair, with Alpinestar 365 X-trafit Gore-tex being my other main pair). I've recently switched to my intermetiate gloves from the alpinestars now that temperatures are often at 6 degrees celcius (43F) in the mornings!

The main reason I'm not using muffs is i'm concerned that should I have an accident that you can't get your hands off the bars quick enough as they'll be trapped by the muffs.