Recently I wrote a post saying I loved the Moses 633 front wing w/380 (old race stabilizer). So naturally (ok, maybe not so naturally) I decided to try the 683/380 combo. I also rode it on the 72cm mast since I had it bolted on after just having riden the 790/325 combo. Rode on a dwarfcraft micro sans straps and 5m wainman kite on 25m lines.
This past Sunday was nukin. I put up my 5m and was lit. I really don't enjoy hydrofoiling lit I've found but went out anyway.
I swear that I could not tell the difference in riding the 683/380 (and I assume that the 420 stabilizer would be very similar) from the 590/330. The 683 felt 20% faster with the 380 (or any of the race stabs I would guess having not tried them). The low end wasn't quite as good as I liked - the setup did stall when when I slowed down too much, much like the 590 does, but on the other end it felt fast, scary fast and was very maneuverable. Really, just like the 590/330. Of course, if you have the 590/330 there would be little reason to own the 683/380 (or other race stab) in my opinion.
If you own the 683 and you want higher speed or variety or more carvability without losing trackiness, I'd suggest a race stab. Again, I've heard really good things about the 425 but have yet to try one.
I think the 683/380 is a little easier to ride than the 590/330, especially on a board with no flotation. I find the strapless waterstart is a little tougher on the 590 - trying to get up to foiling speed. The 683/380 was easier for sure, but not way easier.
The ride was super, super loose in the yaw. It was loose in the roll. And it was loose in the pitch. Not difficult to ride per se, but very loose. On sharp turns on the swell, carving off the bottom and off the top, it never let go once. Some of the flatter stabs required you really lean the board in order to bite and not slide. This setup wasn't slide prone.
Sadly, all the speed got the best of me and I took a hard, high speed toe-side crash on my ribs and will be down and out for a week or so while they heal. Be careful!