I have a few questions on this JIm: What is the material you are cutting? It looks like you are currently using a 2 Flute Cobalt End Mill, correct? What do you mean by the 65mm plunge?
If you are using a 2 flute cobalt end mill then your parameters aren't too far off for a low to medium carbon steel (I'd start at 900 RPM and 110 mm/min). The slower parameters would help but you still wouldn't see too much of an increase in tool life. The best way to increase tool life would be to either use a coated tool or go with a stronger substrate.
If you would like to stick with a Cobalt End Mill then I'd add either a TIN or TICN coating. Either of these coatings would give you better heat resistance and increase tool life for you. TICN would be my first choice, here's an example (1/2" Diameter instead of 12mm)
https://www.toolhit.com/products/01321cc
If you are looking for the longest tool life possible then I'd go with a Powdered Metal End Mill. This is a much harder substrate with better wear resistance than a Cobalt End Mill giving you long tool life (but it still has great toughness). Here is an example (1/2" Diameter as well)
https://www.toolhit.com/products/e9983032tf
Hopefully this helps Jim,
Mike