Monster... I just went through what your doing...
18's will be too stiff and you will NOT like the ride!
Go with 17's. Geno @ LMS can get you Cobra R's with the cool snake logo for $1K
The tires I got have a nice aggressive high performance tread and are ALL SEASON Radials... You live in Wisconsin right??? You'll need the added traction. The tire size I got fits the car perfectly with no impact on speedo. 255/50/17... GO HERE TO SEE TIRE SIZE COMPARE
http://www.1010tires.com/TireSizeCalculator.asp?action=submit
In this size, your amount of sidewall is almost identical to the OEM 225/60/16. You may require a 1/4" spacer on front only to ensure same full turning radius with NO RUB. NO OTHER ISSUES... I got HANKOOK Ventus ST RH06. Check tire here.
http://www.car-rims.com/detail.asp?PRODUCT_ID=hk2555518.
My tire guy here in Edison NJ, sold them to me for $108 Each, that included mount and balance with chrome stems and caps... THE BALLS MAN!
ALL AND ALL for the LOOK Nothing is cooler than those Cobra R's from LMS... Go HERE:
http://www.lincolnmotorsport.com/
Give me a time in the eve to discuss in chatroom if you like. I'll send you some pictures as soon as my job slows down a bit... (Next coupla days)