Not putting down the Z/28 and its LS7 since I almost bought one but decided on a Stingray instead and then the Z06... absolutely no complaints.
The 2 principal factors I like in the voodoo is the broad TQ curve at 3500+ and the high-rev/breathability at the upper rpm's. Plus from all the info so far it seems to be that it'll be a great track and street machine combo with excellent midrange too and it's not just a single-minded beast like the Z/28. The GT350's weight compared to the 5th gen Z/28 is another big factor... no figures yet but it's a given it'll be less. I'm already 110% sure it'll be a huge improvement over my ex-Boss 302 so that's a no brainer for me.
Can't really go wrong with either cars, but for me it's the new Shelby... a better complete all-around package for my preference and moolah.