My primary WAN is a 250/50 and my failover WAN is only 50/5.

This site has about 70 clients. Peak usage usually is about ~100Mbps in the evenings. In a failover scenario, I'd like for PCQ to kick in to smooth out the traffic for the duration it would be in failover.

The only way I can think to do that is to set the PCQ target as my failover WAN2 interface. From what ive read, Ill need to flip the DL and UL max limits. Outside of that is there anything else I should be aware of when setting a PCQ queue on a WAN interface?