World class sprinters run 40s in the 4.3-4.4 range (an analysis of Olympic-winning 100m dash sprinters showed splits from 4.29-4.38), but they lose .1-.2 because the timing begins at the sound of the gun, versus in NFL testing when the timing is triggered by movement off the blocks.
So, yes, the most elite sprinters in the world could run in the 4.1 area, or possibly closer to 4-even in an NFL combine setting. With a full running start, a guy like Carl Lewis probably could have ran 40 yards closer to 3 seconds at his peak.