So I was thinking, shall I buy a new, stiff, car (XXX-S G+), or should I make my Pro 3 a bit stiffer? In the end I decided to save £250, and buy the graphite wishbones.
I'd say there's 1/2 the flex at the rear, and 1/3 the flex on the front - so now the springs move before the wishbones when you use stiff settings!
If anything, I found a little more understeer with the stiff wishbones than before, but the car didn't feel as vague as before with softer springs, and it's definitely a better platform to tune the car from.