David,

I would put back what came with your car, yet from a point of view of "status" 722.5 has just has a handful of parts more, but like Ivanerral said. It does have a 5th gear, and that will complement in fuel savings...

Over one is better than the other to service.. Better than 90% of the parts are identical to 722.3..To rebuild either is basically the same except the 722.3 is a little more complex at the tail portion as it contains a secondary oil pump, and the 722.5 does not..
I have rebuilt a 722.5 successfully, and the weak points are reverse gear on 722.3-722.5 all because a five dollar seal, and B2 piston gets worn form the metal sleeve on the 722.3 & 722.4...
Luckley, the older 722.3 - 722.5 do not self destruct like a 722.6 when things go wrong because the damage is just a seal not an expensive gear parts...

If you have the 722.5 rebuild it your self, or have have somebody like sun valley transmissions(they mail order) do it out of California, but do not put a secondhand unit in as it is just too much of a gamble(work).

Martin