Got any spare 42RH's you'd like to give me? :D
The potential flaw in what you're saying is, that a 42RH may be set up for more slushiness through all the gears, including O.D., for increased comfort … due to the fact that the lock-up feature is available. Meaning, if it has the ability to lock up and make things more efficient and cooler (when locked up), why not make the other gears more comfortable? The reduction of shift shock is important to OEMs. I know, I worked for a couple OEMs in design engineering for hundreds of years. And shift shock was always an issue that was fought to remove or reduce.
Not saying your wrong, but the 300 rpm drop you see (which I know you're right about that), might be more of a drop than I would see in my 727 if my drive gear (1:1) magically had the ability to lock-up (no other changes to the trans).
I'm probably as clear as mud.
7milesout