Generally speaking, more rubber on the ground will give you more outright grip, but the extra unsprung weight will make the car less responsive and will hurt the ability to control the wheels over bumpy surfaces.
It's not possible to predict whether it will make you faster or slower without back to back tests of the specific set ups in question around specific cicuits, so I'm not sure why people are trying to do so. It will also depend somewhat on driver preference / driving style.