what the others said.
if you want, you can play around with some calculators to get ideas:
this one needs tire diameter and transmission gear ratio--
http://www.wallaceracing.com/calcmph.php
for the tire diameter (if you want to see what a different tire does)
http://www.wallaceracing.com/tire-aspect-calc.php
for the 350 TH the trans gear is 1.0, for the 700r4 it is .7 in OD
depends on what sort of driving you intend to do. the 3.73 gives the best acceleration but if you get out on the highway much you might not like it with the 350. I have a 700r with a 3.07. I leave it in D (3rd) around town (tires are 275/60r15)