I stopped by my LRS last night and tried on a black LS Mizuno "thermo breath" compression top that was on the clearance rack. It is tight, of course it has to be On sale for $39, which appears to be a really good price for that sort of thing. It is a blend of wool and different technical fibers that is said to be literally "heat-generating" and warms you when you get wet. They are holding it for me while I make up my mind. I hate to spend that much for a 1-time use before setting it aside for next winter. I also wonder if it might be TOO warm, but is that even possible in low 40's with water and mud involved? Before I decide will hit Target tonight and see if they've something appropriate on the winter clearance rack from Champion. This top is so compressive that I suspect I would still wear something over it.