If you are a 911 man i advise you to wait for the GT 350. It will cost you more but it may also prevent you from dumping it in dissappointment a year after buying it.
Its relativitly man, i can barely stand to be in a standard GT these days after what i have gotten used to so.....
I just drove an 05 911 last week and to be honest, a GT350 will be overkill. Although I suspect it was the actual car I drove, I found my '12 mustang to be MUCH quieter and smoother (well, at least until any bumps are driven over---then the 911 is much better). Powerwise, the 05 felt decent, but certainly not as wild as my mustang at the top of the rev range.
The GT350 isn't a completely different car than the GT--the chassis is a tweaked version of what's in the GT. Power isn't the issue, but feel is. The GT350 might feel nicer then a GT, but it's still not a 911.
If the OP drives a 15 GT with track pack and hates it, he's not likely to suddenly fall in love with the GT350. If OTOH, he likes the GT but wishes for a bit more of everything, then the GT350 might be a good option.