To me, from experience, a full spectrum of plates/bindings on this type of ski can be wonderful, on a spectrum of playful and precise to more race-like and precise.
Probably no relationship, but I wonder what the comparison is between the Head/Tyrolia Speedflex plate and the plastic factory plate for the Rebel WC iSpeed [non-pro]?
The WCR plate is the one used on the Head WC Rebel iSpeed Pros (as seen on the Head website), whereas that lesser plastic plate comes from the factory on the WC Rebel iSpeed [non-pro]. As I mentioned elsewhere, the non-pro with its flimsy plate is the ski Franz Klammer apparently prefers as his main recreational ski, I was told by a Head rep who knows him and has skied with him a bunch, family with family also. (In my experience, it's more playful that way.)
The rep told me Franz turns heads on that ski all day, but he's using it to ski casually, recreationally,
with family and friends, much as the OP intends to use his Stockli SXes.)
I notice on Head's website discussion of the two skis, they don't mention the difference between the plates, just the skis. In the past, I was often told that the only difference between the Pro and non-pro was that plate. Now not sure.
Still, the point here, to me, is that the lesser plate on the same or nearly the same ski can be the best choice for many, including Franz Klammer often, apparently.
To quote Head on the non-pro & Franz Klammer, backing up what the rep told me (and showed me on his iPhone):
WORLD CUP REBELS I.SPEED
DESCRIPTION
The World Cup Rebels i.Speed is the little brother of the World Cup Rebels i.Speed Pro. It features a more forgiving construction with increased edge angles. Therefore, it turns more easily and is more forgiving of errors. Vibration is absorbed better. This gives you a smoother ride and you can launch wider turns. Because you use less energy, you can stay out on the piste all day long. As an advanced skier, you can really get the most out of this race ski. And when it comes to fine carving turns, the ski of choice for Franz Klammer is also your dream companion.
To me, this tends to confirm the OP's sort of plate choice for his Stocklis.