8s would definitely look better on the back with the 255s and I personally would put 7s on the front if using 235I'm sure if I asked nice enough they would send them back, not sure if there is any issues with availability of other sizes.
I could go 15x7 instead but they have the same backspace at 3.76" and then my worry switches to them being too tucked in.
It would look purposeful without being over the top