They are both very good choices. The 270 brass is easier to come by, and you can push 150 grain bullets out of it. In a featherweight, I'd stick with the 270. That said, nothing wrong with the 6.5. I think another option would be to buy an ultralight 260 Rem, which nearly does what the 6.5x284 does, but with less recoil...and benefit of easy brass availability and the short action that is both stiffer and lighter.