ADmakes

OK, I assumed you were trying to push it over 100mm/s..... How do you know its staying at 100? I would try another slicer, if you have the same results in another slicer, then it is your firmware If the other slicer slows it down, then the problem is in the gcode that Cura is producing

what printer & firmware are you using? My first bet is that your firmware has a max X and Y feed rate setting M203 X100 Y100 is what you will likely find

Started using 4.7 a few days ago. On the 4.6 version my print estimation times were always within a few minutes of actual print time. I noticed my first few small prints printed much faster than 4.7 estimated, like 20 minutes to an hour faster, on 2-5 hour estimated prints. Finally did a bigger print last night: Cura 4.7 estimated 11 hours 36 min Actual print time: 7 hours 38 min. This is on an ender 5. it seems the estimates get further off with longer prints. Im glad the actual print time is faster than the estimate, but it was pretty accurate