That's what a minimum spec is for, so you know if the game will even run at all.
The problem is that GZ has the same CPU and GPU requirement for min+recom as TPP does. There are video of people running GZ with a low end i3 and still pushing Ultra/1080p and getting 30-50.
I'm on these: i5 3470, GTX 980 FTW, 16GB DDR3. I expect performance to be around or better than what I already get in GTA5. Which is very good.