[Overdriven]

Fwd will be hunting for traction in the pulling and hillclimb tests, even with weight over the front axle. I agree with the straight axle idea for simplicity. A solid axle with a worm gear drive, or a wheel driving a wheel would be best also. Either would give more ground clearance, since you have only a 1/4 inch from the center of your wheels to the "bumps" you have to drive over.

If you have to have a suspension though, be careful of axle steer. Some link designs have a tendancy to steer the axle when one side is lifted. Not an issue if you hit the "bumps" slow and perfectly perpendicular, but I doubt that's going to happen every time.

Can you take measurements of the course? Particularly "hill valley" so you know what your ground clearance needs to be in the center? Personally, I'd go for maximum wheelbase allowed for the sake of stability over the bumps. Steering settings will also be more forgiving, 1 degree off, a shorter car will steer for the wall faster than a longer one.