Since both the UltraSonic and Phantom Race are nice board when planing, I guess the remaining deciding factor is how much fun are you going to spend when you go riding in non-planing conditions.
Is it possible to schlogg with US147 ? Yes. Is it fun ? No.
Is it possible to shlogg with PR380 ? Yes. Is it fun ? Yes, yes, yes (sorry, never tested PR377 yet).
In sum, are you interested to ride in non-planing conditions or not at all ?