The ideal gear ratio for any condition depends on how fast you want to travel and how quickly you want to accelerate to get there. Both of those dictate the power requirement. You use the gear to operate the engine at or near the most efficient load and engine speed that makes that power. (You need to measure, guess or calculate how much power is required to achieve the acceleration or maintain a particular speed.)
@Jeff88: We covered it in the other thread but those curves aren't a full BSFC map. They are a slice from one edge of one. A guide for what the map looks like, at least close to WOT, but not the full story.
Have a look for a BSFC map, even one from a different engine from yours, that includes lines of constant power. If you understand what that is showing, you will have a better idea of what different gear ratios do. Each line of constant power will pass through a number of efficiency islands. You would like to be in the high efficiency ones.
eg. here:
http://ecomodder.com/wiki/index.php/..._2ZR-FXE_2010-
and read the comments under the Volkswagen Jetta TDI 1.9L ALH 1999.5-2003
The ideal transmission is a CVT, which holds the engine at the most efficient operating point for the requested power. Multi ratio transmissions are an approximation of that. The more gear ratio choices available, the closer the approximation.
For acceleration you probably want something close to an even spread. There is a case to close up the ratios (less difference between ratios) as you get to higher speeds, drag becomes important, and higher power is required to achieve the same acceleration.
If you spend a lot of time at particular speeds i.e. the speed limits, it may be best to select gear ratios for high efficiency at those speeds. It's not going to be perfect because real roads have rises and falls in elevation and wind direction varies, so the power required to maintain a speed varies. You need that CVT or have to accept that you wont always be in the efficiency sweet spots.