Yes, it won't be a problem. You will have "sportier" 1-4 and a nice low cruising gear that you might have to rev up 4th a bit to get into comfortably, but will save you on the hiway. If we assume that you need 30hp (probably a bit high) to go 70mph, then you will go from ~280g/kwh to ~250g/kwh, or about a 10% improvement (if you are like this saturn).
If you make aero mods, the reduced hp requirement will compound in even further efficiencies with the higher gearing (even though load goes down, hp goes down faster, and the lower rpm gearing helps keep the load up).
I started plotting out the hp lines for the saturn, then got bored and just did the rpm range you were looking at, ~2000 - ~ 3500 for hp 10 through 40
