It sure sounds like if you would be craving the exitement of the Formula, or of a large slalom board. With that in mind it is 95% sure that you always will be disappointed in any board that features a centerboard.
The centerboard seems to add some 2 kg in weight, and of course it causes drag. Every CB equipped board is a compromise, and it sounds as if you would not be willing to go that route.
I would guess that the Race 320 and the KONA (315 with the steptail in the air) will feel and taste similarly. Decent glide in light wind, but a heavy feeling in planing conditions (but may objectively still be as fast as any freeride out there). I understand that it is this heavy feeling that you dislike.
With regards to the Rio I do think we are seeing some marketing bullshit. It is positive that starboard has lengthened the board from a barge to something that is closing in on 3 meters. This of course does produce more of a gliding feeling, but I cannot imagine it would get the same glide as a 320-350 board. And while planing it is exiting in the same way as the KONA or the Phantom 301. You need to remember that Starboard has used the same kind of "a revolutionary high performance board" with almost every baord that has just lasted a year in the lineup. That is how marketing unfortunately works...
If the Formula is too physical then get one of the 85 cm wide slaloms. I think that will be a good fit.