I've been using Continental Gran Prix 4-season on my road bike. I use this bike mainly for commuting. I ride this bike regardless of temperature unless it is icy. Then I ride my bike with studded tires.

My question: These tire a pretty expensive (~$65 each) (fortunately I've been able to pick them up wihen the LBS has had a 40% off sale). What differences will I notice if I move down in the Conti line? I currently use the 28mm tires.