I've spent countless hours making those damn Darts go up and down.

I think that a slightly shorter rod might reduce fatigue more than a different reel. At least it sounds like you are probably using a stiff enough rod that you aren't losing a lot of energy just loading and unloading the rod.

I use Diawa Luna's (300 series) and Abu Revo Toro's on almost all my salt rods. The high speed Toros seem to be getting harder to find while the Winches seem to be more commonplace. Get the high speed reel for those kings that get hooked and then come straight up.

Good luck! I'm looking forward to July. A king grab on a dart is one of my favorite things in the world. Stupidly addictive.