The table below show the drag and down force results for the CFD "virtual wind tunnel" simulation of a Mini-Z MR03 Mazda 787b model:
Down Force (gf)
These are average numbers derived from four different simulations, one for each speed, each one of them with more a few thousand iterations. According to these results, drag and down forces increase proportionally to the square of speed, which I believe is what should be expected from the theory.
The numbers are reasonable compared to the weight of the car and are also in the same order of magnitude of what has been reported in other simple homemade wind tunnel tests.