Mike,
I went with Speartech and I believe I paid somewhere around $1800.00 which included the maf, O2 sensors and extended harness to mount inside the car.It is a lot of dough but it was plug and play. Everything labeled nice.
I don't believe the $900.00 GM kits comes with all the wiring? I would say the big thing for me is being able to pick up the phone and call John @ Speartech and get my dumb questions answered. I called atleast 3 times during the wiring/start up of my car. Having the tech support was huge selling point for me. I have wasted plenty of money with parts on my car only to redo it again, but this buy was not one of them. I think if you are good at wiring and trouble shooting go for the GM kit. If not save yorself the headache and go Speartech.
EDIT: I forgot about VVT as that changes things.