Is there a big difference in "wideness" appearance between 235's and 245's running on 8.5 rims?

Well there are difference between 235 tires themselves! Depending on the brand you want to go with. Take a look at tire specs on Tirerack, it will show you tire section width.

Definately fo for 245 or bigger on 8.5" wide rims. And yes the 245's are noticeable wider

I had 245's on the front of mine, and they rubbed on the inside fender splash guard. This was with the stock M contour rims.