A fast CPU will definitely improve the server performance. By default, virtual machines come with one vCPU each. Each cloud server comes with 2 virtual CPU cores. Cloud servers have bursting capabilities and this lets the cloud servers make use of any excess CPU cycles that are available on a host machine. You can ask for more cores. This means if you have 4 cores you can access the CPU cycle 2 double the time that a customer with 2 cores does. But you need to be aware that simply adding more vCPUs will not necessarily improve the performance of the server.