This was my experience going from P zeros to michelin supersports in my other car, though I also went from 19's to forged 21's which were quite a bit wider. The P zeros had plenty of lateral grip, so essentially being pushed into a roundabout there was never any risk of the front sliding out. That remained the same with the supersports, but the car turned noticeably better, so quick direction changes were far superior. But then remember the forged rims were saving a few kg per wheel, and the front tyres were a few cm wider.Lots of people report increased grip with the Michelins, but how much difference do they really make when driving in suburbia, or even on the highway, at normal speeds and sensible driving habits? I'd be interested to hear opinions on this.
The rears (also wider) were where grip was heaps better, the car would lose the back end and step out a lot with the P zeros and that ended with the supersports, though now 25000km and 4 years later, the supersports are losing grip at the back and in fact I had a sphincter clenching moment coming out of my favorite roundabout where the front drifted a touch so I have had to moderate cornering until I get new tyres on and worn in.
But the biggest improvement was actually the ride, sitting on 21's the car rides as well as it had with the P zero 19's which ride a bit hard, but how much of that is due to the lighter wheels I cant say.
I also changed the P zeros on the front of my wife's XE to pilot sports, she is a bit of a car whisperer (and reminds me often), and reckoned it was a noticeable improvement. I have supersports on the Mustang on forged 20's (10 and 11 inches), I think it rides better and handles much better than it does on the OEM 19's which I thought were a bit slushy, and I find it turns really well as long as you put some power down (not so much if you let it coast, it definitely feels the lard and gets understeery), but I think that it came with michelins and I was only changing rim sizes, which I did as soon as I bought the car.