I can see where you're coming from, since the program seemed half-finished at best, but what should I use in its place?
You're probably looking in the ballpark of 300-500lbs of downforce at 150mph, but thats just a guess based on the cars of the era which I found on mulsanne's corner. Based on what I've read about the seven's aerodynamic efficiency, drag is probably quite high compared to these Porsche's:
If you can't manage to find any definitive data anywhere else, then you could try something like simscale's CFD - it's far better than autodesk's software, as well as being free to use. If the numbers seem plausible, then it's probably better to use whatever the program spits out than nothing.