iPhilMickelson: Both also have high trajectory.
AFAIR, all wedges have "high" trajectory, but it serves differently.
And, 5&0 spin is certainly weaker than 3&2 spin. IMHO, that's not a mathematical addition!!
iPhilMickelson: A 75 yd wedge to add between my 90 and 60. I can easily make up the 75 with the 90.
Not precisely that addition (I didn't look up the yardages), but as food for thoughts, what about 65 yds?
Coming down from a 110/115 yds PW in the iron set, it's common practice to equally space three wedges below that
My favourite spacing is 50 - 75 - 100, and other sets have 60 - 80 - 100. It's disputable if the top wedge should play longer or shorter, but it comes down to these thoughts.
Knowing that the punch of quality wedges serves as an almost-equal shot, we get eight full meter shots from four wedges, including the PW.
Look at your punch lengths - do they cover good spots between the full lengths? (might serve for the "68" question) Maybe you don't need a third wedge now.