Well, all I can tell you is that if they're 275/40/17's on 8" rims they don't work nearly as well as if they were on 17x9's. And yes, I run 275/40/17's on 17x9's.
In fact, if you talk to the autoX and road race folks, they typically prefer to run the smallest recommended tire on a given rim, not the largest. And a 275/40/17 is the widest tire recommended for a 17x9, unless you increase the sidewall height significantly. If you're just cruising it doesn't matter all that much, but when you start to push things the large tires on smaller rims tends to make the car feel more vague and less responsive. Not to mention you're really not getting the full advantage of the wider tire because you're squeezing it down to fit the rim. Might as well pay less for 255's and actually get to use the tire you're paying for.