Tons of people running 275/55/20s on QL and non-QL JGCs with no rubbing at all. I'd expect that you should be fine with any tires in that size since you are going with a non AT type tire. I'm running SRT Reps in the same size and offset as the Viper reps. I have 285/50/20s on mine and have no rubbing at any QL height. Hope that helps.
Welcome to the Viper Rep club! I went with the stock size (nitto terra grapplers) cuz I didn't want to mess with the speedometer setting. I've been wondering what mine would look like with the step rails, now I know. Looks awesome. Guess I have another upgrade coming.