It just depends. I have heard a bunch or really good track rats go to oem or other compatible blanks and do well. I don't have any experience with z1 one piece up front but have a set of their 2 piece rotors that I have been tracked for a couple of years. They have performed as advertised. I did have some shutter the last time I ran with them a Chuckwalla Valley. It was with a new set of pads same as what you were running. I think that my experience was due to it being cold temps in the 40s and 50s and 3" brake ducts. Over cooling is not good with aggressive brake pads.
I would take your time and do the brake ducting first. I would also check out Stoptech rotors. I did their 1 piece on my wife's Audi s5 along with their street pads and they are as good as what I run on the Z. Their 2 piece rotor are a floating rotor and are slightly cheaper that Racing Brakes. They are also heavier than z1 but lighter than oem.
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