Ok, so no quantification?
Here's mine: I run a 4-speed 4R100W (evolution of the E40D/C6) and lockup converter behind several hundred horsepower and several hundred ft/lbs of torque off idle, on the street. It makes lots of boost off idle so makes more torque than any normally-aspirated street engine of any displacement I have ever seen or heard of. Lots! According to the sensor, transmission fluid temp stays <190F.
It is no secret that the C-6 based family of transmissions are very lossy. But I don't mind since, like a Cobra, I've got more than enough power for the street as it is. Since we're talking street and not race, my priority is on drivability.
I have enough torque to run a Powerglide no problem. But the vehicle is so nice to drive with the two extra gears and with the converter doing its thing, that I would never dream of downgrading just to pick up some more power.
The advantages of the manual trans do apply to a modern automatic since ideally an automatic would be as efficient as possible and have enough gears to keep the engine on the bubble (and be able to hook up the power in low gear) at all times. The converter is just a different way of slipping the clutch on launch!
Slushbox on a road course, no. The "other" kind of automatic trans, hell yes: some terrific examples that blur the line between automatics and manual boxes are the units in the Ferraris, and the SMG II in the BMW's. Best of both worlds. I still pummel them both regularly on Pacific Coast Highway though!
We'll chat on messenger sometime.
Chris