I was happy to leave it be as the default value.
Some more information:
I have two fiber optic providers, with each having 150mbps connections up/down.
Today, as I was fixing my failover+load balancing issue, I decided to test each connection individually to see where packet fragmentation was happening, and found that one was fragmenting above 1440 bytes and the other was fragmenting above 1428 bytes.
That’s why I changed it, and for purposes of sanity I retained the lower value on both.
As it turns out you cant change the MTU value on the LAN part of the GWN7000 anyways, so this was entirely on the WAN side.
I do have an unrelated issue still to fix, which is that my secondary connection keeps dropping. I’ve set both connections to gigabit Ethernet full duplex but for some reason the fiber modem on my secondary connection keeps hanging - and needs a restart every few hours. Any ideas?