Player rating for tournaments across all installments of Heroes.

The purpose of this thread is to determine a unified ranking system for tournaments held across multiple versions of the game. For example, one tournament might have one stage played on version III, and another stage played on version IV. To create an overall ranking and determine the winner of such a tournament, we need to establish a unified ranking system. This is the core of the problem.

I recently had an idea. What if each tournament in each version awards a certain amount of "currency"? Then, we could establish an exchange rate for this "currency" relative to the Grail (based on the number of participants in each version)? This would eliminate the issue of a winner in a tournament with five players being ranked lower than 40th place in a tournament with fifty players.