True on the balance. You can't balance it for every RPM. You can get it perfect for a specific RPM, but outside that, balance will suffer. I think that most manufacturers shoot for a sorta "happy medium" and try to balance it--not necessarily PERFECT in one spot--but more for an overall balance that works across MOST of the RPM band. Perfect at one RPM may give you uncontrolled vibration at other spots in the RPM range. Not-so-perfect might yield a "acceptable" balance across 90% of the RPM range.