you can tell the difference between vented and solid rotors. well, i could atleast..i took the solid disks off my Jetta and threw some old audi coupe GT vented disks, and it stopped better..
1 reason solid is good vs vented... winter slush/puddles... i had issues years ago on my addy with vented and slush puddles.. they would cool off so fast that you had to get them rewarmed to stop.. solid did not have said issue... so my winter ride keeps solid.. vented is stage 1... 10.1" is stage 2 and works pretty freeken great in old mk1 cars.. some audi 4k quattro calper carriers = same as 16v rocco.. good to go.. 4kq = 84-88 so many more in yards then 16v.. 11" roddo is stage 3... i put them on my kubvan.. i owned the conversion stuff.. for years... they overkill... but throw 1000lbs in the back.. non issue to stop...