Wow, amazing story. And after reading the comments, I seem to have come out of it thinking of John's choice totally differently. John's the 'fuck that shit, I'll have both my sons' type. I read it as John thinking he and Dean would have a better chance of saving Sam (but not knowing how hurt Dean really was) than of he and Sam saving Dean. Poor Sam. In my head, at some point John tells Sam he thought picking Dean was the best way to save them both.