Just so that we keep it all on the same playing field, I think what you're talking about is Roll Center, not Bump Steer. Bump Steer is defined as a change in toe angle with suspension motion. Front Roll Center is defined as the point where a line drawn from the center of the ball-joint (pivot, not stud!) through the center of the control arm bushings intersects the same line from the other control arm. Lowering the front end can push the front RC underground...
Again, as was asked before, if you're not pushing your car (tracking it regularly), the roll center really has no effect on the way the car handles on the street, so why open up a can of worms? The taller stud WILL create bump-steer issues, that then require additional parts, plus a fairly significant amount of time on an alignment rack with a tech that knows what he's doing...
FWIW, Moog makes excellent OE replacement parts. That said, they will wear, just like the Ford OE stuff will. If you price the Ford Racing Cobra control arms, which honestly ARE reboxed GT500 arms, you'll find that they probably cost LESS than the Moog ball joints, plus joint install labor. AND you'll get fresh bushings out of the deal, as well.