I love Icebreaker. Fit wise I think it is pretty normal it I am an xs small in clothes form REI I am an xs from icebreaker. The once caveat is their next to skin line, which I would buy in a s small next time. the next to skin line material is akin to the ibex superfine merino 18.5 line- a bit on the see through side. The oasis crew,of which I own 3, are pretty thick material. Warmer than a cotton long sleeve, but not something I wear on their own in the winter. I think they are great for layering since it has a pretty close/ flattering cut. I usually wear a tank top under them because I think it is more comfrotable- not necceassily a warmth issue. the ignition top is my favorite of all my clothing articles. I love the theumb holes and how well it fits. it even has a drop tail for bicyling. In the winter I don't leave home without it.

For my winter sports I wear, an oasis crew with the ignition zip over it (the pinnacle, tipper, and classic zip are sort similiar but I think the igniton is tighter and more wind resistant- but don't quote me on the last part). I wear my wind proof fleece until I am warmed up and then I take that off and I'm pretty toatsty for the rest of my adventure. layering up like this lets me avoid those periods where I am freezing cold and wicked hot.

I wear wool for my outdoor activities because I can be just as warm without the bulk. personally if I am going to be doing an endurance activity where I layer I prefer 1/4 zips. fewer bulky zippers and I can let off some steam easily.