After reading through this site I finally signed up.
This is a question I've always wondered.
I'll use a unrealistic analogy to make this easier to understand.

Say you have 2 boats with identical setups (we'll use an outboard boat) with the exception of one has a gear ratio of 1 to 1 and a prop of 12" pitch, and the other has a 2 to 1 with a 24" pitch prop. How would their performance differ, if at all?

Now I know because being a HUGE pitch difference could really effect the out come, but just pretend its a closer comperison. I play with "little" outboards, which don't have alternet gear ratios available, and I don't know tipical ratios for engines with this capability.

Just throw out any ideas you have, no matter how trivial it seems.

Andy