Since there is (comparatively) so much room to accelerate at Bonnneville, lead (any ballast really) is generally preferred over aero downforce because it only has a small effect on rolling resistance, where aero downforce generates drag at the square of the speed (ok velocity, if everything goes well over the fixed course, it should be the same thing, just different units).
You reach a point where there just isn't any more traction to be had, a much faster point than this car is likely to go (think Poteet, Main, Teauge, ...) but illustrates the point.
Best of luck, I would love to have it but my car budget is beyond tapped at the moment.
