Pro-Stitcher's feature, Opti-Stitch, allows you "to customize speed and acceleration to get the most accurate stitch for your machine and chosen design. Opti-Stitch automatically calculates the speed and acceleration of the machine to match the chosen design and responds with optimal stitch performance. With Opti-Stitch, your Pro-Stitcher will smoothly slow down and speed up the machine, in and out of corners and curves. Designs will stitch out quickly with excellent accuracy, even with the most intricate designs."
To change the acceleration or speed, select the Settings tab, then Opti-Stitch from the ribbon. In the sidebar, select Customize. When you choose to customize, you are setting the threshold for the highest speed and acceleration the software will allow. This does not mean that the machine will stitch at that speed all the time or even reach that speed - it automatically calculates the best speed for the design you have selected. The same goes for when you are not customizing - the machine will not run at 100% just because it shows that, it will automatically calculate the best speed for the design you have selected, but it may stitch at a higher speed than you are comfortable with, but you can always customize the speed and slow it down. You are the boss of your machine!