im faster in my dialed in acr10 than my zr1 rm with any of the zr1 tunes I have tried, thats all I know. the acr srt10 viper is a freaking beast, and will absolutely dominate if the downforce is ever corrected, however I think its already on par if not bests the zr1 rm.
no sense cryong about the viper, you can tune it to make up for the front down force, the only difference is you will need to use a different tune for top speed tracks and technical courses, which you already have tunes out for the rm zr1 for both events of like the wind.
its all oersonal preference, but the zr1 costs almost quadruple what the acr viper does to own and try...
the zr1 was a colossal let down for me... at least stock it mades for a balanced drift car... and got me a cool paint color I could use on my viper and call it a copperhead haha