It wouldn't be a very good idea to have a double OD, all the stress on the trans with the 2x gear down would cause tons of heat, and obv heat=trans death

 

Yes it's possible.

 

Yup, seen it more than once. But Never with a small block

 

Except that it wouldn't cause any more heat. Heat comes mostly from slipping the torque converter. As long as the torque converter is locking you won't have any more heat. If it is unlocking you ought to be shifting out of at least one of the overdrives.

 

Yes that's what I mean, with such a high ratio you would have to make sure the torque converter is locked, at that point it seems to defeat the point of having the double OD setup because most of the time the GV OD would be used, the trans would be locked out of 4th. I just don't see how the few times you would use it would make that much of a diff with mileage or wear and tear

 

Depends on the axle ratio, the tire size and the engine. I had an E4OD, 33" tires, 3.55 gears and a 351W in a '95 F-150. That setup put me at about 1500 rpm at 60mph in overdrive. It worked great with the truck empty, and I could even use OD loaded on flat freeway runs at 70 mph (1800 rpm)

Now that truck could never have pulled two overdrives, but switch to 4.10 gears, 31" tires, and a diesel and you're up to 1900 rpm at 60 mph. A second overdrive would bring you down to around 1500 rpm (assuming the Gear Vendor has about an 0.78:1 OD, I don't know what it really is).

So would it be a good choice in most situations? Probably not. But it could work out well in some relatively common ones.

 

like an f-super duty with 5.13 gears.