I've meanwhile mounted 4 Michelin 24/61-17 S5B on those 17x9 (tire section is 248 mm and patch width is 235 mm):
http://www.michelinmotorsport.com/Ty...illclimb/Slick
(I was on Toyo R888 245/40 before).
(I was also considering the Hoosier A7 but the Michelin give a slight gearing advantage, are lighter and in the 2-liter-slick-class most slalom races were won on those tires last year (as opposed to Yokohama and Avon - nobody's running on Hoosier here)).
I won't be able to test them before May though.