I can't say enough about shooting 155.5 full bore bergers in a 308. I run a 20" gun and was shooting out to 1250 at STE yesterday. If 600 is as far as you'll be shooting, look at putting a 260, 6.5x47, 6×47 barrel on the gun you have..
For years i ran a 14 power and it worked fine. I shoot mainly 24/25 power on LRP rifles now. I run a 55 power on my 1000 F-class gun. I very rarely go under 40. My 10 year old daughter runs a 42 power and doesn't go below 35.
Below is a one of the videos I made for a small bullet manufacturer to evaluate the effectiveness of 30 cal subsonic hunting bullets. The gun is a 1 in 10 308 running 225 expanding bullets. It's a lot like bow hunting. Just click on the pic