Sadly most of that is wrong or misleading. I'll try to shed a bit of light on some of the statements.
Hi...540 and 550 are motor sizes. They just reflect the length of the can's diameter in mm i think.
The number 540 or 550 is a code number correlated to length, but it is not the length in millimeters. All you can tell from the number itself is that a 550 will be longer than a 540 for a motor of the same brand and type.
If they are both rated at the same kv then they will both perform the same assuming all the other factors are the same (battery, ESC)
Not true. The kV rating tells you how fast the motor will turn with no load per volt of applied potential. However, the 550 will have more torque than the 540 and therefore will turn faster (and pull more current) when under load.
Turns are used for brushed motors. It is a rating scheme based on the gauge of the wire used for the motor windings.
Turns is exactly what it sounds like: a measure of how many times the coil wire winds around each rotor pole. In general, a lower number of turns means a larger diameter wire which in turn means less resistance, more current, and therefore more power.
This rating is irrelevant in brushless motors.
Not true. Number of turns means exactly the same thing for brushless motors as it does for brushed motors. However, a 10 turn brushed motor and a 10 turned brushless motor will not have equivalent kV.
Many have attempted to convert kv to turns but there is no strict conversion. Kv rating states how many rpm per volt the motor produces.
True, there is no strict conversion. You can't say a 10.5T brushless motor will automatically be 3650kV, but it will probably be close.
For brushed motors you might find this decoder ring from Mabuchi helpful.
www.mabuchi-mot...tions.html 
