bainecotec on G6Performance.com that did a custom set up on his ecotec. Because the tranny is the essentialy the same as the v6 (gear ratios a little different) the torque/hp gains wouldn't be as damaging as if the gains were made on the v6s. However Bain is shooting for 275whp, so he will need to beef up the tranny.
That said, if you are shooting for big gains, the price is going to be very high, and would be more cost effective to go with a G8 or other performance car.
As far as the solstice turbo kit working on the G6, I am unfamiliar with the engine codes, but my assumption, (for what it's worth) is no, because Solstice is RWD which would leave me to believe the heads and such are slightly different. But I don't know anything.
Bain stated that his custom setup ran around 2500-3k for the motor work and ecm tuning.
Here's a link to that thread.
Good luck!