Statistical data or function between the time (or speed) to preform a task and the skill level?

Not sure I completely understand what you are after but, speaking as a statistician, it would depend on the expected relationship between time and skill level. If you expect a linear change in time based on skill level then y = ax + c which would be a simple linear regression. If you expect a geometric change in time then model using logs of both sides and still use regression. Your mathematical model should reflect what you expect to see happen as that is what you would then test with your statistics.