Use an online machining calculator to determine the Proper SFM (Based on the numbers from the chart) THEN recalculate the NEW speeds (Spindle and Feeds, etc) based upon the NEW cutter diameter. This is how the system works.
Something I do daily and have never broken an end mill, and I use 1/4 to 1/32 cutters on all material (wood to steel)
It does take a little time to get used to the math, but with a little practice, it will become second nature. NOW once you have the NEW speeds and feeds, AND they work, write them down. For me a Fusion 360 user, I have a home tool catalog inside of Fusion for 3 basic material (Wood, Aluminum, Steel) that contain ALL my cutters. The speeds and feeds are now adjusted, so all I need to do is select a tool and material, and will always have the correct speed and feeds.
It would be SO nice to be able to adjust the Tool Catalog inside of Carbide Create to allow us to also be adjusted…someday.