Just MO, I would keep the car away from him and go with a reputable Porsche tuner if you decide to change your GIAC flash. This will save you money on the long run, many headaches... and save a friendship.

 

Don't do it! Once you start you can't stop!!

 

From what I can tell PES-Tuning does alot for these cars. I talked to my friend that works there and they create all of their own software. He says; Dyno proven over 600hp on X50 with flash and Fabspeed exhaust.

Check out the website www.pes-tuning.com

They do some crazy things for Audi as well.

 

600hp seems unrealistic for only chip&exh. Another concern for choosing tune. If later you want to upgrade to bigger turbos,intercooler etc., do they have experience/customer tests&trials to support your next level? 5G is big for only chip tune. Search around here. You will find pretty good and reliable tuners, Protomotive, Epl, Swizter, Evoms. And they will support for higher mods if you get itchy later(real 700-800hp is simple to them.). Cost should be around $1.5-2.5K.
Good Luck with your mod.