The 223 has largely displaced the 308 in Service Rifle/ NRA high power Competition. You did not specify what type of competition you are interested in but since you said it goes to 600 yards I will guess that service rifle/NRA highpower is what you are talking about. The 1 in 9 twist will do fine with upto 69 grain bullets, maybe more but I haven't tried anything heavier. The RRA in 308 wouldn't be legal for service rifle, Im not sure about NRA highpower (I haven't comepeted in a while and haven't kept track of the rules). Also, I don't think optics are allowed in either class but as I said its been a while and I haven't kept up with the rules. If they are allowed, I would stay at below 18X, I start to see my heart beat above that and it makes me crazy (once again you will need to experiment to see what works for you). I would recommend if you haven't already done so that you acquire the rule book applicapble to the class you will be shooting in before you buy anything, that way you will not spend money on something that you will not be allowed to use.