4:xx mile in running = bike domination with only a few months under your belt if you're anywhere near that sort of shape. I don't care how hard you had to run to get 4:xx - that shows near elite-class aerobic ability.

You should at the least be able to climb with competitive road cyclists right out of the gate with no training whatsoever. It'll take another month or so to get comfortable with the basic handling in a fast-paced group ride, which will probably be more of a limiter for you than the power/issue. I came from running with a much more pedestrian 5:15 mile and that's what happened to me, so you should be a whole level (if not two) above me.

I know a lot of folks will say being a good runner doesn't equal good cyclist, but that's a bunch of bull if you spend even a small amount of time on the bike.

If you're actually as good an athlete as you say you are, spend as much money as possible for your bicycle. Seriously. You will NOT regret it, because you will be riding with/against guys with uber-expensive bikes. Even though the bike only contributes <2% of speed (it's 98% you), you'll definitely get upgraditis when you see all those guys around you on Cervelos, BMCs, etc. With a 4:xx mile, you should go right out and get a top-end road bike.

If money is a big limiter, I'd still do your best to buy a top-end road bike for the reasons above and your rapid rate of improvement, but if there's really no way to do so, the CAAD9 with 105 or similar bikes will be more than adequate, with no real limiter on your performance.