275/40-17 is the standard size for a 17x9. I used to run Nitto 555s for years, and they historically run just a touch on the small size. 275/40-17 555s on a 17x9 will have a sidewall that is pretty much completely vertical with no stretch and no bulge. It looks completely fine.
That being said, I recently swapped over to BFG g-Force Sport Comp 2, and like them a lot more. They look better, are better in the rain, just as good or better on dry road, and so far seem to be holding up better. In the same 275/40-17 size, they run a little bit bigger and have a little bit (not much) of bulge on the same 17x9 wheel. I personally think it looks awesome like that. If I think of it this evening, I'll snap a pic so you can see what they look like. Actually, I still have some Nittos on some wheels also, so I can grab a picture of those, too.