Rick, when you get a chance to get out to your 500 yard area, post up your results. I went out yesterday, with the girlfriend, and shot out to 1,000. Set my paper F class repair center out at 600 yards and fired these 5 shots with the CTR 6.5.
Wind wasn't horrible, but I wanted to tag the 1,000 yard steel plate, as conditions were good, and moved off the 600 yard target pretty quickly. I wanted to put it at the 500 yard plate, but screwed up and set it at 600 instead!! Had that been a 3" target, I would have only made 2 hits. I'm curious to see how your rifles are doing, and which one you decide to use. 308 win is a great choice, but like I said before, the 6.5 will walk all over it. Even at 400 yards, if the wind is an issue..