The way I look at it is, you're already at the bottom of the hill with one of those, so the only way you can go is up
If you don't mind the look go for the wheel covers. Plus I'm guessing with the big tires those have finding a way to push more of the air around them would also help. I found with the Cherokee pushing the air down under more at the front helped a lot. It tends to keep the air from hitting all the nooks and crannies of the under body. The air dam I set up hangs down a little above the bottom of the front axle, so I still have a fair amount of ground clearance, not to mention it only takes about 10min to take off. I know the full belly pan would be awesome, but fair gains can also be had with a separated panel setup.