We claim the ornamental design for a display screen or portion thereof with network speed and throughput graphical user interface, as shown and described.
The single FIGURE is a front view of a graphical user interface for a display screen or portion thereof showing our new design.
The broken line at the periphery of the FIGURE illustrates the display screen or portion thereof, and the broken line showing of text and numbers illustrate portions of the network speed and throughput graphical user interface. None of the broken lines form part of the claimed design.