Not trying to be an ass but do you have data to support this assertion? Except in very extreme circumstances I can't see how you could overcool a transmission.
I don't have any metrics available, but I will say the following in support of my original thesis (wtf am I even talking about here?)
The transmission fluid gets checked while the tranny is at operating temperature. This is because the fluid thins out with temps - the engineers that made the transmission know this and plan accordingly. Seals, valving, pressures etc are all set up for a certain viscosity of fluid. If you never get your tranny fluid heated properly, the transmission is constantly off its game.
Also, you want to get the fluid hot enough to roast out any moisture in it and evaporate it off. Otherwise water can funk up the fluid and break it down. Soudns good, funk up break down, but isn't.
I'd think that if your viscosity was too high (trans too cold) that the flow would be decreased through your valve body & the rest of the "guts" and / or the pressure at a lot of seals just behind these valves & ports would be high, possibly resulting in leaks.
I could be wrong. Maybe a room temperature transmission is ideal. For the reasons I mumbled about above, though, I think you want it to reach 170 or so and spend most of its operating life right about there.
Ok, enough blathering on my part. Time to drink my AM coffee and go to work.
