FYI -Overkill and HPTuners aren't the only ways of tuning 06-08 L32/L26's. ;-)
There's an old tuning source that can tune 06+ without HPTuners (takes $100-150 in tokens per car, plus the fee of the person tuning -Overkill is @ $250+$100core+$30s/h) and so far I'm seeing a lot of improvements in my 06 GT.