I have a Merino base layer that I use for the coldest days. I find the performance similar to my old Sitka Mothwing base layer, but the Merino packs down a little smaller for the back country. If you get cold, both are good options IMO.
I've used a smartwool merino wool base layer (midweight) for cold weather hunting and for winter fly fishing and love them. $60 is a good price for real merino.
I do love all of my merino stuff, but I hear that the newest rage is going to be Alpaca wool, we'll see if it takes off. The guys that push it claim it does even better than Merino in the properties that Merino excels at... who knows???
I've used a lot of merino, and I like it a lot. For straight merino, of what I've used, Icebreaker and I/O Bio have been best, Smartwool coming in 2nd, but still good.
My very favorite baselayers are a merino/synthetic hybrid, Mammut Alpine Underware.
I can see it now, NR big game combo Elk/Deer/Alpaca.....$2000
Icebreaker has the edge on Smartwool, merino is great, and it does take ages to smell of body odour, but whatever you do, dont was it with fabric conditioner, it will ruin it.
Cheers
Richard
Interesting note on Alpaca....I have a pair of Alpaca sox and they wore out very quickly and didnt perform half as well as my Smartwool sox. I have Smartwool tops and bottoms as well and have been very impressed and use them for Minnesota late season hunting exclusively.
It is also interesting that nobody mentions Under Armour. UA in my opinion does a very good job of wicking, but is worthless for warmth. That is where merino wool shines....wicking AND warmth. The only downside I have experienced is that after wearing it along day, you are glad to get it off your skin. Not bad by any means, but it feels darn good to peel it off and put on a nice soft cotton tshirt to sleep in.