Not an expert on 17's, but I'm pretty sure 305 will rub. I think 285 is as wide as you can go on stock rims. I think you can go a little taller but not wider on the OEM wheels.
I know in the world of 20's, people have went up to 35's with just a level. I believe you can even to 34" tall without any modification to the suspension. I don't think going wider is much of an option though with 17's or 20's.