20 or over is criminal speeding in AZ. Totally sucks man about the ticket, I am pretty sure you'd be pulled over under the same circumstances even if a minivan was also going 84 next to you, just my opinion.
Even though the cops may drive 85 on a somewhat regular basis doesn't mean it's ok for the rest of us, safest bet is 10-12 over without standing out in a performance car like ours.
Hell, I go 9 or less, over posted hwy limit all the time, just isn't worth it... Let everyone else get the coupons.
Also, I think by pulling your lic, dl, and ins card out was a good thing, cops don't like you fumbling thru compartments in your car with your hands out of plain sight and especially at night.
Hopefully you can take a class so it's not a ding on your insurance. Be safe and have fun out there.