A 235/7" and 255/8" is a nice combination. You can see my 225/7" 255/8" setup on my website. 4 1/2" backspace on both.
No rubbing problems at all on the front.
The 255 may have some rubbing on the outer wheelwell lip with a 4 1/2" backspace. Nothing major that couldn't be fixed with a little lip rolling. I also have a 5" backspace that I hope will fully cure the problem. Watch out for shock mounts and plates when going this large on the offset.
There are some here that run 275 on the rear. It's got to be a tight fit if the tire ever goes fully into the wheelwell. Also, going up driveways sideways could be a challenge.
I like the black out but it's a personal choice.
Click here to see see my car and hear 5-speeds. http://www.geocities.com/casanoc