[buildbot]

You wouldn’t swap out the crystal, you’d use the internal PLLs to generate whatever clock you want. Much easier!

And you are essentially correct, there is a maximum clock speed for any design, and it has to do with how complex your design is. Essentially, what’s the longest path in your design? Your clock must be slow enough to allow a change to propagate through that path. Pipelining shortens this path by creating registers along it, which are clocked by your clock. When a register is clocked, it stores the value in its input side, and outputs that value on the output side.