Question for you DAn - I have a three-forks 7'6" 3 weight rod that I always suspected was closer to a 4 weight based upon how it casted with different fly lines.
I did your penny test and, provided I measure accurately enough, it comes in at 4.7 weight.
Also, I didn't measure the action but I can tell just by using it that it's among the slower of my rods. The bend goes nearly back to the grip.
For a "slower" rod at 4.7 weight, would you shoot for a 4 or 5 weight line?
BTW - this is an excellent thread -- thanks for sharing it.