Well I have h&r super sports will 245/40r20's(27.7) and it barley rubs so I am sure you will be just fine. mine rubs with wheels cranked in reverse(should have went 35series). as far as 99+ looking slamed it is going to take more than springs to do that. then again everyone has a diffenet deffinition of slammed. my deffinition is the tire rides in the fenderwell.
so even with a 45 series 18 (26.7)you should be fine. most people run 40(25.7 same as stock) series so it does not throw their speedo off. I ike running a bigger wheel/tire combo because the care "looks" lower. then recal the speedo.