I doubt that your machine has enough power to really take advantage of a 16mm tool, let alone a 20mm tool. I'd try to re-sell them and buy smaller tooling.
On our $100K machine, we cut with 1/2" bits at 20-25 meters/min with no issues. I have a 5/8 (16mm) compression spiral in the ATC for jobs that need deep cuts, but I'm afraid to push it really hard as the cutting forces are incredibly high.