You say the cylinders are Worthington HP 100s which indicates a steel tank with a service pressure of 3442 PSI. That requires a larger DIN valve capacity then 200 bar
So completely not true. I have 200 bar valves on almost all of my steels and I regularly get fills to 3600+. As long as the burst disks in the valves are rated to the proper pressure, there is no problem. All 300 bar offers is a few extra threads. I've never had an issue with my 200 bar valves. I prefer 200 bar because it's easier to screw the regs in and out.