The MR53 has
1x 100/1000/2.5G BASE-T Ethernet & 1x 10/100/1000 BASE-T Ethernet (RJ45)
In the install guide for the 52/53 it mentions
Link Aggregation
The second Ethernet port can be used in a bonded configuration with the "PoE" port. Ensure that the AP is plugged into 2 switch ports on the same Ethernet switch that have been configured for LACP bonding. Keep in mind that the maximum bonded aggregate bandwidth is 2.0 Gbps.
Basically just want to team the 2.5 and 1gb connection, can this be done? No = o well, Yes = does that mean 3.5Gbps
or is the 2.5Gbps interface throttled to 1Gpbs (802.1ac V1, unable to use 802.1acV2) and maxed out at 2Gbps when both teamed.