Rubber or Poly for a Daily Driven Corner Carving Street Machine?

I run my poly bushings and stabilizer rod grommets pretty hard and have not had a real problem with them at all besides one that occasionally likes to squeak after a rain.
And to me the extra road noise from them is worth the stability.
The more that stuff flexes means more time that the tires are not running parallel with each other. (deflection) as 72bluNblu says.
The other big ones for putting the tires out of sync is vertical movement and the heavier torsion bars cut down on that movement quite a bit and quick stops when you are playing. :D
Yep, stiffer ride but again worth it for what you get out of it, and the poly flexes less in those stops again keeping the tires less deflected under those loads.