17s all around or 18s in back

Guys, I am looking for some opinions. I am going to upgrade my wheels to get some modern rubber under my car and the old 14 inch coopers are due for replacement. I have decided to keep the small bolt pattern so I am limited to wheel choices and think I am going to go with polished show wheels streeters. Now the question is, do I go with 17 inchers all around or do I go with 17's in the front and 18's in the back. I am planning to go with a 215/50R17 tire in front and would really like to go with a 245 width tire in the rear. If I go with the 17s I will use a 245/50R17 and will mount it on a 7 inch wide rim to get the 6mm offset the streeters have in the 7 inch wide rim. The tires will fit pretty well dead center in the wheel well. If I go 18 in the rear I would like to fit a 245/45R18 but that size requires an 8 inch wide rim and the streeters only come with a 0 offset in that width. The 18 inch tire has a slightly smaller section width than the same width 17 due to the shorter sidewall but mounting to the wider rim pretty much cancels that out and it will fit standing still but will not be centered completely in the well and I will have only about .75 to a .5 inch to the wheel lip which may cause problems. I really like the look of the wider 8 inch wheel in the back showing more wheel lip but I am not sure I like the idea of the tire being so close to the fender lip. I would like some advise on what you guys think. I have put up some pictures of the car it is pretty well bone stock with a factory 8.75 rear and kh discs and sway bar up front. I am trying to modernize the look a little and like the style of pro touring cars but want to make sure the car can go back to original. Just tired with the stockish look for now so I added some fabricated valve covers under hood and think some new wheels and tires are needed to change the vibe of the car. Let me know what you guys think of the staggered 17/18 look. Thanks!