I can't help with questions 1 or 3. In fact, I would like to know those answers myself, I hope someone has them.
As far as question 2, I have a 67 daily driver with 3.08's If you don't have an overdrive tranny, then your RPM's at 70mph are probably around 2700 aren't they? If you were to go to 3.73's your RPM's at 70mph would jump to about 3400. For me, that's not the stuff of a daily driver. I think 3.08's are kind of a good balance between daily driver and kick-***, as you put it.
I recently installed a 5 speed with a .68 5th gear ratio. Now I am considering a deeper rear gear, although 70mph is now only 2000 rpm. I get about 20mpg at 70mph!