Those tires will be roughly 1/2" different in overall height from one another which may mess with your ABS. You could run 315's out back and they'd be OK.
Nope, the 255/40 is only 25" high and the 315 is near 25.7. I was just in this situation myself and had to go with 245-45-17 to match my 315-35-17. Look on nitto's site at their tire sizes, it shows the different sizes and their overall diameter. It will help steer you in the right direction.
They fit but they look like a$$ IMO. 245 45 17, 275 40 17 and 315 35 17 are all the same hight. I had 245's on 9.5's but didn't like how it looked so I went with 275's. I liked the look but they would rub the swaybar and I didn't like the way the car drove (at least for me). One of my 17X9.5's was faulty so I got them to replace it with a 17X8 and they sold me another at cost ($200). So I went with the stock 245's up front. The car looks and drives great.
Scott
P.S. Sent you a PM