Using percentages as far as performance really doesn’t work. It is exceptionally arbitrary as there are so many variables to sound quality and every person values different aspects.
Is it worth it, is a value judgement based on your desire for better sound and your income level. I own a $22K amplifier because I can afford a $22K amplifier…OK, let’s be honest… I can afford a $10K amplifier… but this is a disease so I bought one more expensive than was prudent.
If I could afford it I would own an amp in the $40K range, I would… in this case the own the ARC REF 160m I have that my friend lent me. I know the performance of both these amps very very well… they are sitting in front of me. To me the more expensive mono blocks are worth it.