3.73's in my 70 Hemi Challenger w/ 275/60x15's & a 4 speed and just did a 1300 mile cruise. 70-72 mph at 3500 rpm gets old fast! And trying to "go w/ the flo" at 75-80 means cruising at 4000+ RPM. Go to pass someone & you're at 5000 RPM. Too much wear on the motor, IMO.

I may switch to 3.23's as did my friend w/ his T/A. He likes the hwy ratio much better than the 3.91's & its got great acceleration, too. I tend to agree. At 70 in 4th gear, I was busting the tires loose at sea level w/ the Hemi & 3.73's & think the motor's got enought torque to smoke the tires w/ 3.23's.
I'd think your choice depends on the power band & torque curve of your motor. But if its a street car w/ only an occassional street race, go w/ the 3.55's. That way you can enjoy the freeway as well as a burnout or two.