A6 2.7T S-Line HP w/ Mod

I have a LEASED '04 2.7T S-Line and am looking to get more performance out of it. I have seen on this board that the GIAC chip could really change the car and I am leaning towards this but I do have a few questions:

1- Does the Giac Chip comprimise reliability of the car? Have people had many problems with this chip and turbochargers, headgaskets, etc?
2- I was told that the chip is not detectable by the dealer if you also buy the stock program with and switch it with the remote transmitter back to stock before service. Is this true?
3- I was also told that becasue it is a lease NOT to bother getting the Tiptronic Chip because that one is detectable. Anyone have the GIAC ECU Chip and not the Tip chip? If so, how is the combo?

Many thanks............