In general, with increasing internodal distance the propagation velocity increases. The reason is, that in the myelinated part of the axon the propagation is only electrotonic. Electrotonic propagation in ideal enviroments is on average 1/10 of lightspeed. At each internodal intersection an action potential is generated. This takes at least 500 zo 1000 microseconds. But, there is one caveat. Electrotonic propagation decreases the amplitude with increasing distance. If the internodal distance is to long the propagated depolarisation will be beneath the action potential threshhold and at the internodal intersection no AP will be generated and propagation wll stop.