I have the GT3 bar in my NC, and I run up to 245/40-17s on my Weds TC105N wheels, which are 17x9+49. There's no sign of rubbing on the backing plates for the rear legs of the bar. I do have the bolts in "backwards," with the heads in the wheel well and the nuts in the cabin. If you run +45 offset, you'll be 4 mm further away from the inside of the wheel well. I have pretty high spring rates, but my car is also very low, so those factors may offset each other.
2009, STR & DD. 1995, HPDE. 2004 MSM, sold. 2010 Mazda3, hers.