It would be interesting to understand why you did not like the Phantom and the Hybrid Carve. They do have the CB you are looking for, but obviously they are still missing something...
I don't think that switching from an older formula to a new one will change anything dramatically. There will for sure be come performance increase while planing, but non-planing cruising is likely to be worse, if anything.
I have not tried the Phantom Race 320 myself, but it sure sounds like a decent compromise for you. That is, if the priorites 2 and 3 have any value (subplaning cruising and teaching). On the other hand, it sure will feel different from a Formula when planing (i.e. heavier).
I have extensive experience using a KONA which I do think would feel quite similar to the race 320. It is clearly narrower than a Formula which means that it actually feels more like a freeride board (slightly overweight), both in the straights and in jibes. The value of these boards come from the fact that you use them in subplaning conditions, or to tack out from a bay that makes shortboards impossible.
But a Formula will of course plane a lot earlier, and is the correct choise if planing windsurfing is the only thing that counts.