In Scandinavia they are selling winter tires that have even less RR. They are called something like Studdless friction tire, I think at least some versions are sold in Canada too. They are less noisy, more comfy and give better mileage than normal summer tire. On the other side, the rubber material is designed to be used mostly in temps under freezing point, so in SF area they'll practically melt down on heavy highway use on a sunny day. I have used them (Bridgestone Blizzak) all year around in my golf vr6, and they decrease fuel usage about 2mpg -> normal summertires and about 5mpg -> previous stud wintertires I had. Despite that Finnish summerday temps are usualluy around 70F, they work OK if not driven too hard. Not too sporty, though
P.S. These are bit different than winter tires (or all season tires) that are sold in mid-Europe. These are better on snow and ice and worse on tarmac.
Ari