727 Transmission Efficiency...

That is a really good explanation. I have some vague images of a torque converter in my head from seeing such images on the internet. But I've never taken one apart. To me, the whole converter and automatic transmission is magic and wizardry inside a metal housing.

I'm getting my mind wrapped up into replacing the tachometer. Right now its a vintage Suntach? unit. Most people like these, I guess for the nostalgia. But I'm not really down with it. And it's located above my left knee and I don't like that either. I'm wanting to upgrade the tach and put it and the AFR gauge up on the dash.

I run a 42RH overdrive trans with converter lockup in my Dart and can tell you that when the converter locks up the RPM's drop 300 rpm's pretty much on the nose.
I can also tell you that when it is in lockup it feels just like a stick in high gear, as it has that same direct drive feel through the drivetrain.
In the summer I also notice a drop even in the engine temps when in lockup since that is where they cool best as already mentioned.