To me, there seems to be four basic possibilities. 1: Approximately linear 2: Somewhat like a parabola 3: Approximately asymptotic to some upper limit. 4: Initially somewhat like a parabola & then approximately asymptotic to some upper limit. 5: Other The 4th seems most likely to me. Perhaps other Posters would include more possibilities. It is likely that some or many others would disagree with my opinion.