Ok back to the concern of wheel width being uber important... Would it be silly/dangerous to put a 10.8" rubber on a 9" rim? (ie. 275mm on a stock 9" rim) - since the stock rubber is 9.6" wide (245mm) - would this make the rubber flop when doing turns? Point is what are the advantages of going wider (275) as opposed to stock (245) - just cosmetics or what?

 

Not dangerous. 275 is rated for 9" rim. Cosmetics and more rubber on the road.