agreed that good tyres are a must. surely though good 205's or good 215's will be better than good 195's?
you can't compare good tyres against rubbish ones!
It depends...
I'm no slower on 195s than on 215s because you can push 195s to the point of sliding, as you get plenty of warning it's happening, and can make the car move about a bit - which I like.
Whereas on 215s, you have so much grip that you push on with one eye looking for a soft verge in which to position your accident...as you have little warning of when the car is going to let go.
you can go too wide...so wide you ruin the way the chassis behaves...and it just gets numb.
Grip...then nothing.
Much of being quicker A to B is to do with confidence. If the car is doing what you want, and you know exactly the amount of traction and grip you have...you relax, and drive quicker.
Always being aware that you have no idea where the limit is, isn't relaxing...so can be slower.
Of course, on a standard suspension GTI you'll have scraped the door handles and crashed long before you run out of grip, regardless of the tyre width fitted.