You mentioned max D is 330'. Is that a consistent 300-300'? Or a "I yoinked the heck out of this one and got it to 330' but would have a tough time replicating the shot..."?
Either way, one disc I recommend is a Pro Leopard. It could be one of your regulars very soon. It does well both at 100% and 75% power and definitely has more than 330' distance potential. Learning how to throw hyzer flips and turnovers with it will be useful even if you're not using it for max D, and it is a good disc for both form work and the course.
If you want a max D disc, I wouldn't be surprised if a Tern worked well for you. There seems to be general agreement that it's a speed 12 that works relatively lower for "lower speed arms." Speeds 9 & 10s, particularly Valkyrie (maybe Pro or flippier Star), but also a Sidewinder (Star?) or Heat, also seem like decent options.