Which tire size would you guys get....

255 40 17's or 255 45 17's...I am basically looking for the maximum amount of contact patch as possible with an 8 inch rim....the 255 40's have a 10.3" section width and the 255 45's have a 10.1" section width and there is only a 4 dollar difference between the two(at least with the tires I am looking at)

One tire will throw my speedometer off one way and the other set would throw it off the opposite way....do you think the 255 40's are too small of a sidewall?

Thanks guys