I think we are gonig to end up comparing apples and oranges here.
Marathon = 1500 turns vs 500 for normal.
The Marathon player, will be getting 3x the benefit of the IW than the guy at normal speed, because that's 3x the bonus in the same time-line.
If he wants to move the worker from point A, to point B, he gets 3 extra movements where the normal guy only gets 1.
Test this for yourself by running a race around your kingdom, or from one end to the other.
The problem is that the Marathon player will not be receiving 3x the benefit since improvements take 3x as much to build.
Since there are 3 times as many marathon turns as there are normal turns, we'll consider expending 1 normal worker turn equivalent to 3 marathon worker turns.
Scenario: 5 adjacent forests in which it takes 3 turns to upgrade on Normal speed, 9 turns to upgrade on Marathon speed (no, it's not anything specific)
Worker:
Normal speed - 5 turns from moving into the forest and doing nothing else, plus 5*3 turns to upgrade = total of 20 turns
Marathon speed - 5 turns from moving into the forest and doing nothing else, plus 5*9 turns to upgrade = total of 50 turns
Fast Worker:
Normal Speed - NO turns wasted moving into the forest, plus 5*3 turns to upgrade = total of 15 turns
Marathon Speed - NO turns wasted moving into the forest, plus 5*9 turns to upgrade = total of 45 turns
How much you've saved:
Normal Speed - The Fast Worker made you save 5 worker turns (20-15)
Marathon Speed - The Fast Worker made you save 5 worker turns (50-45)
However, note that 1 normal speed turn is equivalent to 3 marathon speed turns. Converting it (so you're comparing apples to apples, so to say), you get that the Normal Speed Fast Worker saved 15 marathon worker turns, while the Marathon Speed Fast Worker saved 5 marathon worker turns. Therefore, the Fast Worker is more effective with quicker speed.
Taking your data that normal speed is 500 turns and marathon speed is 1500 turns, we observe that the only way the fast worker is better than the regular worker is when moving into forest (or hills) tiles. On normal speed, you save 1 turn, which is equal to 1/500th of the game. On marathon speed, you save 1 turn, which is equal to 1/1500th of the game. Therefore, the Fast Worker is more effective with quicker speed.
Need I say more?
