Well, I'll tell you I had the same delemma (sp?) I had to run lines into an outside wall for a kitchen sink instead of going through the floor to the basement. I ran copper to a set of valves and used sharkbites to connect the pex. A nice sweep into the wall up about 20" to a copper 90 and out to the sink shutoffs. I put insulation between the outside wall and the pex. I figured PEX would hold up to freezing better than copper, since the pex will flex and the copper won't. I live in Michigan and we've had some cold weather this year!