Wow! A whole lot of great info here that i was looking for! Hope you don't mind me asking (and i have very specific reasons) but is there an easily-swapped/reliable auto that will work well behind any of these. Will a 4T60 bolt up? Or are there special electronic interfaces needed like with a 4T60E?

A 4t60 or 4t60e will not bolt up to an Ecotec. Wrong bolt pattern. Maybe there is an adapter available but I do not know. I have a turbo on my 2.2 and would like to have an auto but none of the Cobalt SS models that I have seen came with an auto. The auto that came with the 2.2 is not very strong I have been told. When I bought my HP tuners kit, the auto cavaliers and cobalts were not supported so I stuck with the manual f23.

I thought I posted earlier, but I guess it didn't take.

The 2.4 in the G6 came with a 4T45E or a 6T40E.
I know nothing about the 6T40E, but the 4T45E also came bolted to the 220 HP 3.5 V6. (The 4T65E was resserved for the 3.9.)
My 3.5 G6 w/4T45E has held up quite well, although it's "torque managed" to death. I also don't beat on it.

I suspect it would do okay in an Ecotec Fiero, especially with a stock ECM tune. Although it won't do anything (like shifting) suddenly.
But since it's going in a 600 lb lighter car, you might be able to tune out some of the torque management and other "nannyware", and make it a bit more fun.

I was looking at the latest HP tuners supported vehicles list and with very few exceptions they now support automatic equipped cars. So that opens up quite a few more potential donor vehicles .Now I have to find out what transmissions came with the 2.0 turbo cars I might be interested in.