3.73 in 4th Gear with 25.7" tires = 65.8MpH @ 2250RpM
3.42 in 4th Gear with 25.7" tires = 71.8MpH @ 2250RpM
3.73 in 4th Gear with 28.9" tires = 74.1MpH @ 2250RpM
3.42 in 4th Gear with 28.9" tires = 80.8MpH @ 2250RpM
To paraphrase my Questionnaire
If it's your daily driver, or your only car
If you drive hundreds of mostly flat highway miles a week
If you don't race competitively
If you don't want to upgrade the driveshaft or the torque converter or the valvetrain
then you'll likely prefer 3.42 and will not NEED 3.73.
Had a wagon, very close to OE except for 3.42, for about 2 years. BEST MOD EVER.
Having driven several 2.56 2.93 & 3.08 B-cars, 3.42 should've been OE, in spite of CAFE MpG tests.
Had a 9C1-LT1, very close to OE except for 3.73, for about 2 years.
The more highway miles I drove, the more I preferred 3.42.
Luckily I didn't need to upgrade the driveshaft.