Unfortunately I am not a tuning wizard and can't offer suggestions as to which spine to go with. But, I will encourage you to chase that 600+ grain arrow you want given you can get it to fly great out of your bow. I too have had a specific goal in mind when it comes to my set up. I have found that so much of this sport, passion, hobby, whatever it is to you, is mental.
If you're not confident in your setup then doubt creeps in and screws the whole thing up! Find someone who can help, preferably in person. I did and have been able to find my "setup confidence". Don't settle for just ok. Get what you want in a setup you can shoot well. Then practice, practice, practice, practice, etc.
-Jeremy