First, welcome to H-M! You should be able to find answers to just about any question you may have here. Feel free to post about your projects too!
I cannot say that there is a prescribed speed for sanding or any other abrasive operation. Many small belt sanders have a 4" drive wheel mounted on a 1725 RPM motor, giving a speed of 1805 SFM. Naturally, the faster the speed, the faster the removal of material will take place, and the more you may create sparks when sanding ferrous materials.
I have always been of the belief that faster is better when it comes to grinding or sanding. Slow speeds just create a lot of heat without removing much material. I believe faster speeds will also tend to give you a better finish than slower speeds, especially if a little finesse is used.
Many of the high end belt sanders run belt speeds up around 3000 SFM, and some even run 4500.
I guess the choice is yours.