You've raised a very important perspective that I had neatly side-stepped in the above discussion (hey, it was windy and sunny and I wanted to sail..).
Quite often it does take a certain amount of time (or familiarity or understanding) to find and dial in to get the best out of a new piece of equipment - and the casual "jump on at the beach and go for one blast" test does not always show the true potential of the equipment (new or old) under test. The HyperSonic example is probably one of the best in recent memory.
( a more current - and relevant - example could be seen in the DFC, where the old straight rockerlines benefited from sliding the whole board onto the plane and being sailed relatively flat [longitudinally] ; the DFC tends to be better with a bit of a kick and then weighting back onto the tail. Old flat rocker guys (the rocker, not the guys, Salty sit down..) may initially not relate or not prefer the slightly "wave board" feel of the DFC in marginal planing. But (on the other hand ) a "DFC familiar" guy will be comfortable with the planing technique, really dialled on how to get the best top end from the DFC ride and also (then) feel that the front of a (older) flat rocker (non DFC) board isn't riding so free (at least not as readily) as what you can on a DFC. These are minor differences, but the difference in the ride is clear enough for any experienced rider to notice - either actively or even subconsciously. At least after a couple of sessions.)
Obviously boards like FU93 vs ST93 are significantly closer to each other, and as such the differences are more subtle, and in turn fully "dialling" in on these to extract the new "best" (both by style/technique and tuning) often is in turn a more protracted, subtle process than switching between radically different boards (or sails or fins etc etc) where a quantum difference smacks you right in the face - and forces at least a fundamental change on the spot..
Varying usage conditions too, can highlight a variation and make a difference clearer (or alternately cloud it, if not complimentary to the new design)
The real test is indeed after a few good sessions and suitable dial in/familiarity time: at that time, do you wish for your old favourite, previous "comfort zone" back again ?? .. Or are you satisfied (even against your own beliefs) that the new option really is better - and despite previous "vows", you then really don't see yourself going back.. Sure, the old gear still works (and some of it super good, eh ?) but there is progress too, and even if all of it is not everyone's dream, the average for the sport is pretty clear over the years..
And for a lot of guys, chasing and understanding and comparing and mastering these subtle changes is a vital and interesting, even compelling aspect of their windsurfing. No, it's not for all. But quite a few!.
Enjoy smoking Salty, but watch out he doesn't smoke you.
He might be old and the ST93 likewise, but it's a rocket in it's own right,
and driven the right way, still good to keep FU93 owners honest
Should be a great shoot out. Keep us posted. Send pics !