I was originally going to do 17" wheels until I found out that would add $5k to the build cost. Ultimately I decided on 15x8's up front and 15x12's in the rear with the +4 flare's like you. I'm also having RCR do the body fit and have asked if they can install the +4 flares slightly lower to accommodate my 24.5" diameter rear tires: Pirelli Pzero 345/35R15. I went with this tire b/c it is the only DOT approved tire that suited my need for fat rubber on a 15" wheel that's Y speed rated. As an added bonus, there is a matching set of appropriately sized 225/50R15s for the fronts.