I bought Continental DWS06 245/45 earlier this month. It actually doesn't look that great to have the rubber sticking out past the rim. Going with a 40 series might stretch them a little, but 255 would look silly. If I had it to do over I would get the factory size 235/45. I can't tell what the range penalty is yet since it got cold right as I changed tires, but given the clear increase in traction it's probably significant.
How do they ride compared to stock? How about road noise?