Anybody running 17" Cobra Bullit rims on a Duster

Yeah I really don't care if it looks wrong or not, you are losing performance.

Some places won't even mount them up because they're out of the recommended range. And even though the section width might still be wider than a 255 the tread profile still isn't right. You'll probably also find any warranty provided will be voided, for both wear and damage.

Better to stay in the recommended range. Cramming a wider tire just to say you have a wider tire doesn't accomplish anything. I do run the minumum width rims on mine, which still isn't ideal for handling. But it does give you a little edge protection on your rims. And since my cars are primarily drivers I'm ok with that. But I wouldn't try to put a set of 40 series 275's on an 8" rim. My 275/35/18 fronts are on 18x9's, and my 295/35/18 rears are on 18x10's, and I wouldn't go with rims narrower than those for tires that size. Realistically I'd probably be better off with 255/40/18's and 285/40/18's.