Guys & Gals, I ran across this video by Winston Moy at Carbide 3D. It is a video offering feeds & speeds for acrylics. He used these recommendations for the Shapeoko 3 but with testing is a good starting point for the LongMill. As with any outside source, test and make adjustments as necessary to prevent bit problems. The link for the video is at the end of this post. Winston does make some comments about the reasoning behind his recommendations, especially the 1/4inch end mill. Worth watching. The numbers are listed in the video and description but I created a spread sheet which I will also attach.
Youtube Link: Acrylic Speeds & Feeds for Shapeoko - #MaterialMonday - YouTube