Ddon't know if you think this relevant but I once saw a Dung Duster (Agricultural Fertilser Spreader) that was parked at the time. The Horizontal stabiliser, it was a tail dragger, was caked with at least an inch of mud on 90% of the leading edge. The acft had obviously flown in this condition, from memory it was a Pawnee, perhaps they are a very forgiving acft.
The point is its not just ice that will affect the aerodynamic efficiency of your acft, but any for of solid contamination.