In reply to An Triubhas:
I've had a few Merino tops and have mixed views on them. I think they're great for cool days, but find them far too hot for warmer days, and they don;t actually wick that well IME, they also get a bit damp and heavy I think, especially for something like running.
The best tops IME are Patagonia's Capilene, and the merino mix tops like the Rab MeCo.
I get by with 4 styles of base layer top for all year round: a tshirt, a long sleeve tshirt, a zip neck long sleeve top, and then a Patagonia R1 hoody..