For the official feed-speed chart:
http://carbide3d.com/nomad/feedandspeed/
only titanium and steel are suggested to use coolant.
Folks have used a variety of coolants — WD40 is featured on one nifty drip system (on a Shapeoko 3), Apollo grabbed some synthetic coolant used on the Haas for his titanium multi-tool cut: Nomad Made: Custom Titanium Multi Tool