I drove a friends 05 6.0 around for while, Hooker headers, a "custom" cam(No effing lcue what it was), high flow cats, x pipe, intake, 540 crank on a dyno, was a fun as car. Stock suspension, handled pretty well and the ride was a little stiff - but as it was only for a couple of weeks I never got tired of it. On a lighter note, I had a MazdaSpeed3, it was comfortable and I liked it, but it got old after less than a year.
Think about gas mileage as much as anything man, I say buy you a nice SI or Jetta and let it right(I vote SI, great little cars and arent stupid expensive)
Anywho, the GTO isnt that horrible on gas, I got somewhere around 17 city out of the 6.0 that I was driving, and although some people run 87 it will give you a bit of a knock - I would suggest to run the 93 octane.
The Jettas are turds, as well. Ran one in my stock Mazda, he had about three grand in the motor - boost controller, turbo back, intake, bov and an upgraded intercooler IIRC - he still couldnt do anything //content.invisioncic.com/y282845/emoticons/frown.gif.a3531fa0534503350665a1e957861287.gif, he was about heads up with a late 90's GT
Best of luck in your decision, if it was Me I'd buy me a 4 cyl Honda Civic and build me a street rod
That's what I"m getting ready to do, I'm putting my nice audio off for a while
Sorry for being long winded.
Also - what exactly appeals to you about the GTO vs the GLI?