Merino is a very cool wool. I have, however, stopped using it as a base layer for biking because the long climbs here make me sweat a bit more than usual. For mtn biking, I wear a pack and merino does not wick as well so my bak feels cool and damp. For road biking, it works better but on long climbs, I still get the same effect, though I sweat less than most. For example, I NEVER drip sweat and my helmet never gets soaked or anything.

I use merino for less strenuous activity like hiking easy flat rides in cold weather. I'll use it as a base layer for easy runs in cold weather too. It insulates well and keeps me warm. I also use it as a second or third layer...I have tops in several thicknesses. In general I love merino but not as much for cycling.