if this helps you, you can determin chip load by dividing your feed by your spindle speed...
spindle speed= 3500
20/3500=.0057 (per rev) now divide this answer by the number of flutes on the end mill you will be using (2,4,5....)
.0057/4=.0014 (per flute)
how much you can increase your feed rate also depends on the rigidity of your tool and setup.
Remember, the only time your tooling isn't wearing is when it's cutting air.
Liter, faster cuts aren't more efficient but, sometimes that is the best the machine will do.