Personally, for max distance purposes, I think you're better off adding a faster, less stable disc than a slower one, especially a slower more stable one. Something like a PD is going to add little if any distance at ~300' of power, and moving up to an incrementally faster understable disc like a Valk likely won't net you enough extra D to make an impact.
I added a distance driver once I was throwing fairways around your distance, maybe a little longer on average. After trying a few options out I ended up using Laces. Max weights are pretty stable at your power but a mid 160s won't be, and they're easy to find down to 150 class. One of the lighter ones will almost assuredly net you more D, it's just a matter of finding the right weight. The Sorcerer and Tern suggestions (especially a Star Tern) are along the same line as the Lace.
Trying out a max speed disc will give you a true sense of whether you're able to get separation from your fairways or not - which is the purpose of adding a distance driver in the first place, right? - and will also maximize said added D given you find the right disc with the right stability. There are enough max speed discs out there built for your power to find one that does this.
As an aside, I also feel as though adding an understable distance driver at around your power has several positive effects on your game. It teaches you to see distance lines, allows you to learn a lot about release height, and also introduces a difference kind of touch disc. My max D Laces, for example, are definitely finesse discs that have taught me a lot about hyzer releases at certain release heights. Distance drivers are definitely not for beginners, and can do terrible things to your form if used incorrectly, but once you have some experience and decent D they can be a positive addition to your bag if used correctly.
