Would you feel more perfect by following a sudden switch or reversal of standards? I'm here to say I've seen standards evolve and devolve with time. So, in the end, what determines perfection?
I think it bears true that you should always examine why you perform certain tasks the way you do, and why you are required to adhere to certain standards. So you take a long, hard look at what you impose on yourself, and what you believe others ask of you. Sometimes the very act of practicing the task will lend you the answer. At other times, say, a teacher will explain the reason for the standards at hand. And other times, the value of the standard is already self-evident.
One way to determine whether or not the drive for perfection has become unhelpful is by examining its goals for practicality. What is the practical purpose of the perfectionism? Is the purpose obtainable, economical, adaptable, or functional? Perfectionism that ceases to exhibit these qualities begins to step over the line from healthy ambition into obsession.
Raising the bar of our expectations and application of skill does not always lead to perfection, and, not all perfectionism is maladaptive. Many variables enter the stream of life every time we attempt to score, say, 9 out of 10. Inability to accept a well-earned 8 can be the kind of perfectionism you don't want to keep. Sometimes it's difficult to accept the idea that you're right where you're supposed to be with your skill set at the moment. This leads to the kind of dissatisfaction that goes with maladaptive perfectionism.
This is one of those subjects that can widen in every direction. But in keeping it simple for now, I will conclude by saying, keep perfectionism in check by always honoring the practical. And be willing to reevaluate the value of the practical by measuring it against perfection.