Two things to keep in mind.
1) to pull more Gs without the ski sliding up out of the groove it's carving you have to tip the ski more.
2) Tipping the ski more dials up a tighter turn, and an even tighter turn with a smaller radius ski.
The longer radius GS ski can hold the line at speed to pull a high g-turn when tipped to or beyond the needed critical angle. Tipping a SL ski to the angle needed to hold that high G GS turn, will have it dial up a SL turn that it can't hold.
This is 100% right, though I've pretty much given up on trying to explain this particular concept.
Basically if the pressure angle (angle from the center of mass to the ski edge) is higher than the edge angle, then the ski is inherently unstable at that edge angle and speed. It will either high-center you or skid out of the turn.
If a ski is unstable at all "feasible" edge angles (i.e. all edge angles that you have the technique and strength to achieve) then that means you've exceeded your speed limit on that ski. The interesting thing here is that a stronger skier can typically make stable turns on a given ski up to a higher speed than a weaker skier.