If it were me, I'd hie me to the nearest Michelin dealer and get whatever tire corresponds to a 255-section, 45 ratio which I think is the largest that can comfortably fit on your 8.5 rims and has the same diameter as the stock tires (27"). The oversize tires will have to carry less weight per square inch of contact surface, so last longer, but will take a bit more power to push, so will use more gasoline.
My experience with Michelin has always been good, beginning in 1964 and extending to the current tires on my convertible. I think Michelin have the ability to design a good compromise among comfort, sticktion and durability. Expensive, but worth it.
ADDED: 2014 GT 5.0A conv. black: electronics, comfort, security, CA plate (FLICK U); assembled 06-13-2014, delivered 09-25-2014; odometer today (03-21-2016) 4,321.5(--> DELETED --> 2013 5.06M coupe, black:: Odo LAST day (09-25-2014) 7,975) (--> DELETED --> 2008 GT/CS: Odo LAST day (10-22-2012): 9,719.3; #2075 of 2509 convertibles, #560 of 718 in Ebony. 2009 GT/CS: Odo last day (09-08-2012): 12,000.1; #34 of 1705 coupes, #3 of 377 in Performance White. <-- DELETED <--)