AD9516-1 use VCO or bypass?

I have generated the required clocks using two different configurations of the AD9516-1. One mode uses VCO, divides by 2, and thus I need a higher input clock frequency. The other mode bypasses VCO, and thus I can use a lower input clock frequency.

Is there an obvious advantage to using one versus the other (phase noise effects) ? Should I always use the VCO when possible, or always bypass the VCO when possible? Or should I just try both and see which gives the best results?

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