I've been rockin' the Base 2.0 stuff for all my winter activities (snowboarding / skiing / shoeing) for the past few years. The 2.0 works wonders if you're getting your sweat on, but if you're just lounging around the campsite, you're gonna need something a bit more substantial. I skipped over the 3.0 and went right for the heavy weight stuff.
Paired with my Patagucci R1, I stay nice and toasty in this combo. Size wise I went with a Large (6 foot 1 @ 162lbs). I also wear a size large in their 2.0, but the 4.0 feels a bit more snug fitting.
The 4.0 stuff is always quite pricey, so catch it on a sale or when they are blowing out last years version.