You need to keep in mind that changing tire size the way you are considering will throw your speedo calibration off. Changing the tire diameter has the same effect as changing the rear end gears.
In order to put a wider tire on and keep the same overall diameter you have to go with a shorter aspect ratio. In your case that means going from a 40 to a 35, and the size closest to your stock diameter is 295/35. If your stock rims are 19x8.5" a 295 width tire won't work very well. A 285/35 is the next closest size, and still close enough that it shouldn't put the speedo off by too much, but a 285 is still just a bit more than a 8.5" rim can handle. You can physically mount it on the rim, but it probably won't look right with so much tire extending past the rim with such a short sidewall, and it certainly isn't ideal for tire performance or tread wear either.
You could get away with going to a 275/40 on that rim width (even that size has a minimum recommended rim width of 9"), but you'd need to have your pcm reflashed to correct the speedo.
I need to ask what your goals are in changing tire size, because going from a 255 to a 275 isn't going to make a huge difference, either in grip or visually, so it seems like a lot of trouble and $$ without much pay off.