Unless you're really sold on these wheels...my suggestion would be to keep shopping. If you're going to stay with 18" wheels...then get a set of 4 that are all the same size. If you're going to go with a staggered set-up...then upsize to 19" or 20" wheels where you have more choices for a set of staggered tires.
When using staggered wheels...you also want to stay within 3% (+/-) overall circumference/diameter on axle-to-axle and/or side to side. Going over 3% (+/-) can screw-up the ABS/DSC/AWD calculations and systems.
Using a simple tire calculator site (1010tires.com)...I found two 18" staggered wheel/tire set-up within the 3% variance:
- 255/55/18 (fr) 265/50/18 (r) - Nitto NT55 tires (-2.10% diameter variance)
- 255/55/18 (fr) 275/55/18 (r) - Michelin Lattitude Touring tires (2.98% diameter variance)