For 6061 I run everything at 4,500 RPM, I use 2 flute polished HSS and some Atrax carbide. I am not so happy with the carbide, but HSS leaves a really good finish. I spray the end mill with WD-40 and then dry machine with an occasional air gun blast to clear chips from the on-coming end mill. My parts turn out very clean with no chip welding issues at all. I generally run 8-12 IPM on the feed and 30% DOC based on mill diameter. I always leave .004-.006 for a finish pass and run that climb cutting at 8 IPM. I also try to stay around 40%-45% stepover when pocketing.
BlueFin CNC LLC
Southern Oregon