I would sure like more grip on some of the sweepers I encounter on track.
Sorry I can't help with suggestions. But I'd like you to explain more of your analysis, if you have any to offer. The point being, more down force comes with more drag. At lower speeds neither has much effect. Whether it helps or hurts on a track depends on the track, whether there are fast sweepers vs. tight hairpins and whether there a long straights where higher drag is a liability. Consider, for example, Oak Tree followed by the long straight at VIR. The turn is so slow that you'll get little benefit from drag, no lower transit time and no higher exit speed, but higher drag will cost you on the long straight. In contrast, a shorter track with a carosel, for example Summit Point, would seem to be benefit from more down force without paying much drag penalty.
I've never driven them in competition, only worked them decades ago. But that's how I remember them.