I put out huge amounts of heat. I literally steam in cold weather. If I'm moving uphill, I'm sweating even in below freezing temperatures wearing only a light, base layer T-shirt.
Some observations. Merino wool is good for moderate sweating, as it doesn't stink, and has decent moisture management. However, if I sweat a lot, the amount of moisture will eventually overcome wool's ability to trap the moisture, and the garment becomes soaked and sodden. When this happens, it takes wool a relatively long time to dry. This is because wool relies on being able to trap moisture in the fibers, using body heat to turn that moisture to vapor and move it away from your skin. Overload wool's ability to trap moisture, and it ultimately stops performing.
Compare that with a wicking synthetic, such as Patagonia's Capilene. (Don't use polypropylene. There are much better modern alternatives such as Capilene made from polyester.) Unlike wool, synthetics are hydrophobic and don't absorb much water. They keep moisture off of your skin by having fibers where the very outer most layer is hydrophillic (absorbs water) but the fiber core is hydrophobic. (Note that this is the opposite of how wool works.) The result of this is that a synthetic moves moisture away from your body by moving it along the surface of the fibers. Performance wise, this means that it will feel more clammy than wool for moderate sweating, because less moisture is trapped by the fibers. However, under very heavy sweating, synthetics work better than wool, because they don't absorb as much moisture into the fibers, so their "wicking performance" (the ability to move moisture away from your skin) doesn't get overwhelmed. A synthetic base layer that gets soaked will dry many times faster than a wool layer that has been soaked.
What does this mean? It means that if you can avoid really heavy sweating, a merino wool layer is best. It will keep you less clammy, will have less body odor build up, and will regulate temperature better than any current synthetic.
However, if you know that heavy sweating is inevitable, a synthetic base layer is best, as it will continue to wick even when soaked, and will dry much more quickly than wool.
For your particular situation, I would wear a lightweight synthetic baselayer, and nothing else on your torso, while moving uphill. When you get to the top of the mountain and your exertion level drops, add an ultra light windbreaker to prevent too rapid cooling and evaporation.