Ran into the same thing on a VF-2 with 6061 a while back. Book called for around 6000 rpm and I crept it up to about 6800 with a .5 inch end mill and it cut like butter, no chatter at all. I usually watch the load meter first, keep it around 70 to 80 percent on roughing, then double check with chip color. If the chips come off silver with a little straw tint I know I'm in a good spot. When they start turning blue or purple I back off, meter or not. The book numbers just get you in the ballpark, the machine tells you the rest.

Wow, so did the scale ever teach you anything useful, or was it all just noise?

Did you ever find those 2 months in the code or did they stay as lost as my first deploy?