RE: Difference between Giant, Mammoth and normal scale?
In the USA, "large or giant" scale is usually considered to be IMAA rules - 60" for multiwing planes, and 80" for single wing planes. There are, of course, planes that are MUCH larger than this. Take a look at some British websites to see really BIG planes.
It's relative and subjective, depending on your experience and outlook. My Fokker Dr.1 is IMAA legal at 72", and is allowed at "giant scale" meets, but it certainly is not a large plane, by any standards.
Dr.1