I don't agree - have you ever tested out high-speed burners to see what speeds they actually achieve?
I did just that recently with the
Samsung USB 18x (not for the first time, I might add) and the results show that you really do not achieve anything like the claimed burn speeds.
That's because, in the main, the burn strategies used meant that data isn't written at top speed except towards the outer edge of the disc.
But all is explained in that review.
So, being highly practical about it, I'd not be worrying whether a burner I just bought didn't burn at 20x or didn't burn at 18x or didn't burn at 16x - it will burn fast enough (and too fast for some operations - when you're better off burning at slower speeds, creating movie DVDs, being one instance).
More important - is the burner good enough? And I suspect, from my experience with the Samsung USB 18x, is that what you've just bought will actually be rather good.