Per Dave Gilbert at Performance Auto Werks the auto tranny is quite beefy. The auto transmission is also used in the Cadillac CTS, STS and SRX. The SRX is a SUV that tips the weight scales at 4,442 lbs and considering our Kappa cars are just a little under 3,000 lbs the transmission should hold up fine up to 400hp in our cars.
There is a transmission tune that allows it to shift harder and at higher RPMs than stock, if an even sportier drive than OEM is up your alley. There is an "i" gear (1st - 3rd) that's a blast to use on a twisty mountain roads, 3rd gear really has balls. The auto tranny has torque reduction software built in (that can be removed by the tune) that prevents it from using as much torque as what the manual tranny can use (or at least that's how I assume it works).
I've read of manual tranny users that can peel out in 1st through 3rd in their cars; don't expect to do this with an auto...it ain't gonna happen (although I've read of the TCM tune allowing a chirp of 2nd gear).
Auto transmissions are typically a hair faster in a drag race (at least with other cars).
I had to get an auto because my wife wanted to drive the car. I've been happy with it (even though I would have preferred a manual).