Cowboydoc,
Not to worry. You can't go wrong overbuilding. /w3tcompact/icons/smile.gif It occurs to me that those big old houses you see were all built with rough cut lumber and most of them have lasted a hundred years and will probably be here a hundred years from now. The new stuff with milled 2x4's--well, the jury's still out.
Much better to build a little heavier and not have to worry. That barn should last you a long time. /w3tcompact/icons/smile.gif
SHF