the 10 inch wheel will give you a "wider footprint" this mean more tire will be acutally making contact with the ground...which is a very good thing.
always go with a wider wheel when you can...even the Outlaw 10.5 guy's who must use a 10 inch tire are putting them on 12 inch rims and flattening out the foot print.
in your case there would be No advantage i could think of by using the 8 inch rim...go to 12 inch wheel if it will fit under your car.
Brian
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Bjuice..
"I'M YOUR HUCKLEBERRY ! "