I'll leave this links here that might be needed later as helpful resources & remember to read this carefully:
Speed of electromagnetic waves/Electromagnetism
in a vacuum (No air) is
about the Speed of Light (The fastest speed possible).
Link 1:
http://www.physicsclassroom.com/mmedia/waves/em.cfm
"An electromagnetic wave transports its energy through a vacuum at a speed of 3.00 x 108 m/s (a speed value commonly represented by the symbol c)."
Link 2:
http://www.bbc.co.uk/bitesize/standard/physics/health_physics/using_the_spectrum/revision/1/
"In a vacuum, all electromagnetic waves travel at approximately 3 x 10^8 m/s - the fastest speed possible."
Speed of Electromagnetic waves/Electromagnetism
through air (representing the insulator) is
Relativistic+, at minimum it's sometimes Relativistic:
https://en.m.wikipedia.org/wiki/Speed_of_electricity?wprov=sfla1
"In everyday electrical and electronic devices,
the signals or energy travel as electromagnetic waves typically on the order of 50%―99% of the speed of light..."
"...and
almost that fast when air is the insulator."
Speed of electronmagnetic waves/Electromagnetism through matter
is Relativistic+, at minimum is Relativistic (dependent on what matter it passes through):
http://www.bbc.co.uk/bitesize/standard/physics/health_physics/using_the_spectrum/revision/1/
"When electromagnetic waves travel through matter (for example, light through air or glass), they travel a bit slower than this but rarely less than half as fast as in a vacuum."
Speed of an Electron is about Sub-Relativistic:
https://education.jlab.org/qa/electron_01.html
"A calculation shows that the electron is traveling
at about 2,200 kilometers per second. That's less than 1% of the speed of light, but it's fast enough to get it around the Earth in just over 18 seconds."
The speed of the return stroke of lightning is Relativistic:
http://www.maine.gov/mema/prepare/prep_display.shtml?163524
"The return stroke (the current that cause the visible flash) moves upward
at a speed of about 320,000,000 ft per second or about 220,000,000 miles per hour (about 1/3 the speed of light)."
^ The Speed of the Return Stroke of lightning mentioned here is travels around 0.3c (Relativistic):
https://en.m.wikipedia.org/wiki/Lightning?wprov=sfla1
"The rate at which the return stroke current travels has been found to be around 1×108 m/s."
The speed of the Step Leader of lightning is Massively Hypersonic (Read the last paragraph & look at the diagram on the right):
http://www.lightningsafety.noaa.gov/science/science_initiation_stepped_leader.htm
"While the stepped leader develops
downward at a speed of 200,000 miles per hour, the leader would move much faster if it didn't pause between each of its steps downward."