I was in the same boat as you just a few years back. I was using my exact hunting set-up to start, 3 years later I considered taking the next step. We have a 300 league not a 600 league, but same difference.

With my hunting setup then, 70lb PSE Mach10 w/Scott Mongoose release,I maxxed at 296/297 for average. I have shot pistols competitively so I think that helped me. The true "Target" guys would of course shoot 300's and be counting X's with 58-60 x's being not unusual. I had the opportunity to wade in with a borrowed Pro-Tec from a pro Hoyt shooter with a back tension release, 30" stabilizer and 8x magnified site. After a ramp up time, I was shooting 300's as well and chasing 60X's throwing a few outside the x regularly. After a season.... I personally went back to my hunting set up. I enjoyed the target bows and the 300's, but I found for me, it was kind of like that Super Hot Chic in college. She looked great, and all the guys wanted to be with her. Well, then you take her out and she won't shut up, she wants to go home early and sit on the couch and watch Sex in the City and thinks beer gives you bad breath. My point is it wasn't asas good as I had envisioned it would be. For me, being almost perfect with my hunting bow felt more rewarding and was tougher to maintain then 300 was with the target bow. That being said, if you are interested in attending and competing in some of the awesome archery shoots that NFAA and other orgs host around the country, defintely dive into it. It can be a lot of fun and with some devotion you can and may do well on a big stage. It just takes skill and a little luck in a 2 day shoot to break the elite barrier once. It gets pricey, but all the good hobbies are it seems. Just think about "why" you want the bow first. If you think it is because shooting 600 is cooler than 557, it maynot be worth it. If you want to be the best shooter in the house, and feel like competitive archery may be something you are interested in, go ahead and do it.