i'd say keep the speed limits the same, but on change those stupid electric signs that read "motorcyclists, you are all speed demons. we gonna get ya" to suggested speed (not limit) for conditions.winter/summer limits as well as commercial/civilian limits on highways.
well ideally it would be like france where the limits change for rain vs clear skies. our govt's too cheap to buy signage like that so a blanket change for winter conditions would be better than nothing. as it stands, i think our limits take into account all negative factors and that's how we get severely low limits.