I went through that same dilemma about 4 months ago. I was actually dead set on getting a used z06 until the new 5.0 came out. Getting a BRAND NEW gt exactly how I wanted it just worked out better for me. The Z is better in just about all perf. categories but for the money I had the gt was just a much better deal. Plus its def. no slouch itself. I love it and still glad of my decision. GL.
i see you are in Raleigh, were you on HPJunkies? I went to NC State and graduated in 2008. Had a black 03 Mach 1 and hung around with the HPJ guys, did some detailing on the forums (name was "smbstyle")