Check out the LS1GTO.com forums. I'm not trying to jack your thread, but I pretty much stopped using this site because they have much more Austin people there. Also, there is a gathering every Saturday at the Home Depot at 1431 and Parmer lane. Always get some Goats there. The Austin Goat Herd is the local club.
In answer to your question, Mothers does good work. We have had five cars tinted there, including the GTO, and always like their work. I have metallic tint on my 05, and radio reception changed very little. AM reception went down a little because of the lower signal strength than FM, but you wouldn't even notice otherwise. Get what you want, you won't be unhappy with metallic. They offer lifetime warranties and do a huge volume of installs due to good quality and reputation.