yeah you have the basic idea, just 'ups' the final gearing, ie slower pull away but slightly better top end, also lowers revs when cruising.had the range diffs in the widow, but changed back to series ones as i prefer the standard gearing around town, at 30 with range diffs i had to use 3rd, can now select 4th at 25mph with no snatching.
Down to choice.. I didnt notice any differnce in fuel economy either..