1-2. Speed and FC won't have much of a difference since yung overall tire size mo na bago will be 30.6", assuming you have a gls model. medyo may difference lna nang konti sa speedo mosince iba na yung rolling diameter nung tires. ma compare mo yan if you have a GPS.
3-4. performance wise, well.... it does serves it purpose if you spend 95% of your driving on paved road but ok pa din yan sa mga dry unpaved road.
5. Looks: well depende na sayo yan sir. some like to have a low profile look na medyo bling and some like thier rigs to look mean and tough. ang importante is at the end of the day it's still our personal preference that counts.
here are some reviews that might help you:
Nitto Dura Grappler Tire Reviews and Info,
Dura Grappler - Highway Terrain Light Truck Radial