Keep in mind though if you want to get the most out of wicking fabrics, you'll want to get shirts that fit close to the skin. Fabrics that hang loosely won't be able to absorb sweat and wick it to the outside to evaporate as efficiently.
To put it another way... picture spilling a small glass of water on your countertop. Is it quicker to wipe up the water with a towel that's laid flat (close-fitting) over the spill, or with one that's bunched-up in a ball (loose-fit)? The one that's laid flat is going to absorb the water more quickly. The water can also spread out more quickly through capillary action, which in turn increases its surface area to help it evaporate faster.
It's the same idea with wicking fabrics. To perform at their best they should fit properly. The colder the weather the more important wicking and evaporation become.