With the price of fuel fluxuating so much these days and not knowing where it's going to end up, the 410 gears are a little to much if you want fuel economy. Mid 300's as Techinspector suggests is a good highway combination for a TH350 Turbo..
Take into account that you're going to be running an overdrive tranny which, if you go with too low a gear ratio, ( below 370 ) the end result could be that the engine rpm's will be too low for the torque converter to function properly and vibration in the drivetrain may occur.