What is the highest and most optimal MTU for Bonded Internet connections?

The highest maximum transfer unit that System Force Bonded ADSL can support is
1600 bytes. That is also the most optimal MTU for Bonded ADSL Internet connections.
Anything higher than 1600 bytes will require fragmentation of those packets.
However other service providers (Such as AOL) only support an MTU of 1400 bytes, so we reccomend a maximum MTU size of 1458 otherwise, you’ll encounter connection problems and slow speeds, an overall degradation of your service.