Hi, I built my zen quite some time ago, it has been a good solid printer, although now I have two other printers, so I am returning my zen to a CNC configuration
Anyway I run mine at 25mm/sec max, with 1000mm/sec^2 acceleration and xy jerk set to 5. Works nicely at that.
If I try to go faster than 35mm/sec it starts to loose steps.
I found a good steady print speed is 20mm/sec perimeters and 25mm/sec travel moves and infill. for good quality solid prints.
If I want speed I use my Delta printer
If I want accuracy I use the Zen.