Things I have sussed.

Kress at full power, 25000rpm
320mm/m feed
2 flute Alu Power 4mm cutter
1mm depth per pass
A mixture of lemon juice, old engine oil and water squirted into the path makes an excellent cooling/lube
Gantry cnc's are awesome

I've had zero snaps and cut 4 brakes out with the same cutter.

Hopefully someone will read this and find it useful.