Hi,
To answer your question about the available clock speed for the i7 processor being used in Surface Pro 4, it ranges from 2.2 to 3.4 GHz. If you would like to know the exact speed of your Surface Pro 4 processor, you may check dxdiag.exe, this tool will help you get the information of your device processor. Please follow the link on how to open and run DxDiag.exe.
Let us know how it goes.
Regards.