[Ironangel]

The 3:07 is a 3:08, just as the 3:08 in many cases is referred to as a 3:07. Car, truck, standard or automatic, it doesn't matter, they are the same. Davepl pretty well clears it up with the varying tooth counts, there is no such thing as an exact 3:07 or 3:08. I think the "three-o-eight" won notoriety because it's easier to say than "three-o-seven".
Tim is correct in that although the eight lug Dana 44's are referred to and matched with 4:11 Dana 60's or 4:11 14-bolts, it's actually a 4:09. No gear set is dead nuts, you can call it what you want, but the terminology will forever be a 3:08, it's just easier to say. Besides, a 307 is a motor not an axle.
Harpo your correct in that it dont make a difference, and incorrect because you never change out just a ring gear or pinion. They are married sets lapped together from the foundry, when one goes the other must go with it.
LockDoc is also correct in sharing his experience with OD transmissions, six cylinder motors and high geared axles. Cant compare a 5000 LB panel truck to a 3000 LB later model unibody. GM did not put 3:08 axles behind six cylinder trucks for obvious reasons.