Why was the crucifixion necessary ?

[Drich]

Yes I get what your saying. Jesus was tortured and executed so that we may have "an idea of the cost of salvation/atonement."

This does not address what my question is.

I'll try and put it in a different way.

If the worst possible way of execution at the time was being "hung-drawn and quartered" would that be the method used to execute Jesus.
Was the "worst possible way known" chosen to make the most lasting impression on the witnesses.?

There were still Prophecies to full fill, but I do not think it would be much for God have changed them to match the death of Christ whatever the method.

If the aim was just to make an impression, couldn't something else spectacular have been done (i.e. turn the sun off for an hour - that way everyone in the world would get the message).

the sun was "turned off from the 6th to the 9th hour." and look how that has impacted you. You weren't even aware and yet you still knew of the crucifixion

Was it the execution that was the essential element - regardless of the method - or was it the method that was the important thing? To both these questions I ask why?

Yes Jesus HAD to die. Why? Because we are told God established the standard that any and all sin deserves Death. Righteousness demands that someone die for the sins committed against God. Jesus was that death for those who accept the offering made on their behalf.