Usually i cut around 60-70% speed (mainly cause I'm a newbie) but different blades will perform differently depending on material/thickness etc. Ive never cut at max speed but I'm also mainly using softer woods plywood,birch,pine,sometimes oak at 1/4,1/2,3/4 inch thickness.
For me its when i start over-forcing the piece into the blade instead of letting the blade do the cutting. I will also speed up the cutting 25-50% to what i had when i originally started cutting with the new blade. That's the hint its getting dull. They go in the "used" test tube for use on another day when my supplies get low