Fast Corner estimation for older devices

I would be surprised if it's that much, but yes it's a lot. You might also try compiling a an APEX design(closer in process) and look at two paths for the min and max models, just to see what the spread is. Probably half is more realistic. But it's certainly possible that you can get shipped something faster than your slowest speed grade, so that's going to cut into your margins quite a bit right there.