The performance impact of multiple extents is historic, not a myth. The amount of time to move from extent a to extent b is nothing today. Fifteen, twenty, twenty-five years ago that was not the case; the amount of time required to move the head and await the rotational delay could be the difference between acceptable and unacceptable.

I can tell you from experience, if you've gotten your burnt by something it's real difficult to 'put it in the past'.

FYI. Try uniform extents, it's a lot of work up front, but saves a huge amount of work later.