? gearratio c-4 dailydriver

Trying to decide on gear ratio of 89 Mustang 2.3 turbo c-4 intercooled. Still has original 3.73 gears. Approx 3000 rpm at 55 to 60. needest to say not good on gas. This is daily driver for wife. Tire size p225/60r15. Shifting is between 3300 to 3700rpm. The way I read I need to stay under 3000 to stay out of when computer changes loop modes. Don't want to do this several times. Have done several search but most comments are for 5 speed or dragracing with a c-4. What do you recommend.

Thanks Stinger I found that calculator. But didn't know motor would do at differant gear ratio's. Thought changed at 3000 been reading Turboford I've been wrong before. I won't be running no 75-80 if I am I want care about fuel mileage. I was thinking of 3.08 but with your advice forget that. Would something around 3.27 or 3.45 be good? Wife drives speedlimit . We live within 5 miles of work and not too much out of town.New at the 2.3 t but trying to learn. Definitely has a learning curve.Thanks alot save from one gearchange and money. I respect your opion