I found AHS had better plumbing pieces than morebeer.
Also, regarding 1/2" or 3/8". I don't know that the increased price can be justified by the performance difference. Especially at 50'. From what I have seen most immersion chillers will do about 10 minutes for a 6 gallon boil.
So regardless of the diameter and surface area discussion, the question is which one actually cools faster, and by how much?
I use a 50' 3/8" IC and I it takes 11-12 minutes to cool to 65-70. I would find it hard to believe that a 50' 1/2" would do too much better than that. Unless someone told me that it was 0-5 minutes for a 50' 1/2" I don think its worth spending more.