It's gonna be more stable w/o the FEL on for this simple reason: No matter ballast or not, the FEL is going to transfer weight to the front end, so the rear end is going to be lighter than w/o the FEL. When you transfer the weight off the back end, you have put it on a pivoting axle that, even if the front wheels stay on the ground, allows the tractor to lean downhill. So you have less weight on that solid up-hill rear wheel and less stability.