I just got the same exact tires in last week I'm just waiting for my weld wheels to come in. I haven't used the et street r's yet but they have the same technology as the et street pros and they are fantastic tires so i am hoping they will be just as good.
I've always had good luck with ET Streets radials but on this car not so good. I have 305/19s and over 700 hp. I suppose this GT500 with this much power and not enough weight on the back end may not be a good combination. On asphalt I spin them at over 60 mph.
Mostly stock just borla atak catback, jlt resonator delete tube, passenegr side oil seperator lol. No tune dynoed at 624/631 to the wheels. I figured i have power so i need the mods to put that power down before adding more power.