I‘m not sure what your driving skill levels are, but from the perspective of someone who likes to exploit a car’s handling, but is not necessarily competitive at doing so, (I’m pretty stoked if I can pull off a really nice heal and toe) I will give you that perspective:
I had a “fast street“ 74 spider that I would occasionally auto cross, and at my skill level I was able to consistently go quicker in that car with the rear sway bar Installed. However, with my GTV, and the same basic set up, I was quicker without the rear sway bar, and more notably, I felt quicker. The point I am making here is first related to Don P’s comments about “feeling more controlled, but not necessarily quicker”. Although I am sure he is right, at my skill level I am able to go “my quickest” with that controlled feeling.
That said, i also think the differences in handling between the Spider and the coupe are inherent enough that in my opinion the Spider did not gain the more controlled feeling for me that the GTV did, when removing the sway bar, and that’s why i could go quicker with it.
This of course also concurs with what others have said about how subjective it is. Add in tires, wheel size, unsprung weight, etc., and this paints the clear “formula” picture also mentioned by others.
The only other thing I would add is just that IMHO, short of high-end full-on race cars, whatever you do these cars are far less the quickest handling, but rate much higher up the scale of fun handling cars, -for me, and my regular Joe skill levels at least!