I have used both printers. They both great in different fields.
Under my exp.
Z6200:
Super productive due to it's printing speed
Excellent color but if you want to use a RIP, it might be a little bit confuse due to the CMYK+ONLY Red
Good for large sign printing
The blade are so so only, it CANNOT cut a lot of materials such as thicker paper or canvas
It doesn't take "too thick" paper such as Hahnemuhle Photo Rag Pearl
iPF8300:
Very Good color reproduction
Very Fast as well
It takes almost any kind of materials
The blade trims almost everything
If you use a RIP, CMYK+RGB is even harder to get it right
I prefer the Z6200 for your business because
1. Speed is more important for you
2. The color gamut is big enough for your type of jobs
3. The 60" wide machine is a beast
4. If you get the 60" one, you can perfectly expand your business to large format poster field.
Hope my information would help you a bit
Aaron