based on his response i would say you need an additional .25 spacer on front and back (assuming you still have the 1" one in the back) if you want to go with the 9.5 width and 38 offset and have a chance of running a tire that wide as his 255/40...unless you go like 245/40 which will help a little as its shorter tire and little more stretch to clear that fender when its coming down,lol.
just remember to keep a connection with the width and the offset...just switching to 8.5 wont mean anything if the wheel you find has a 20 something offset.
this website always helps me compare where im at (put in your current setup) and then different options to see where you loose (or can gain) some space by playing with wheel and tire specs. Online Wheel and Tyre Fitment Calculator. Offset, Tyre Stretch and Speedo Error | Will They Fit