My '92 GSR had a 4.4 final drive and a shorter 5th gear than either the LS transmission or the '94-'01 GSR transmission. 80 mph in 5th gear was about 4600 rpm or so, and I got fine mileage on the highway. Cruising at high rpm with low throttle opening doesn't use a lot of gas.

That said, I can think of plenty of other mods that can be made to an LS before I would go into the transaxle and start changing gears. The reason it's so easy to change axle ratios on trucks or muscle cars is because they're actually in an AXLE that is separate from the transmission. Drop the rear end, pop the housing, swap a couple gears around, relatively little fuss. On a fwd car with a transaxle it's much more of an involved process.