I just had a look at the lms mill, i see that it's a 500w motor, from my experience (limited take with pinch of salt ;-) ) on my mill which has a 750w motor. I found that moving down in what seemed a very small amount in size of end mill made a massive difference for me. I try to keep to 12mm (1/2 inch) or smaller cutters, i can get away with a 16mm cutter but it's always a bit more on the edge of being ok.
In my case it might be a machine regidity issue as it's a round coloum mill.
You may find theirs a sweet spot where you can maximise the cutters ability to cut vs the machines regidity.
Regarding the better end mills, i try and save my cobalt up market end mills for steel where i definetly see an improvment over regular hss mills.
I've got into the three flute end mills quite a lot but have only used them in smaller sizes, very handy for slots etc. as they cut a bit faster than two flute.
Stuart