@Chrysalis - Agreed, PPPoA is indeed far superior. For the one case of 1500-byte long IP packets, now I have woken up to the use of VC-MUX (having rid myself of the idea that it didn't work with BT and PPPoEoA), at least it is just the same as PPPoEoA VC-MUX anyway, because of ATM cell padding. But for many packet lengths, especially short ones, the difference is massive.
The thing is, it isn't quite so simple, the Firebrick may need the config options provided by the use of PPPoE interface objects, in order to define the upstream rate policing and it uses PPPoE I suspect to detect downed interfaces so that it can do failover - it will shift the traffic load seamlessless and very very quickly over to the remaining i/fs or fire up a failover interface such as a 4G USB dongle.
So I might be completely ruining all the reliability and load-balancing feature of the FB.
There's possibly a lot to lose just to get the MTU fixed. And after all, I never had the joy of MTU 1500 in recent years. I lost it when I gave up using an integrated modem-router with PPPoA (my beloved Netgear DG834 v3) and went to separate-box modems because unless you are using a Draytek Vigor you've had it for MTU 1508 on 20CN as I found out after I bought my first DLink modems having used ZyXel separate modems before that. So all during my 20CN days, while I had a separate modem, I was stuck with MTU 1492 PPPoEoA.
Make sense? I would need to ask RevK (with his Firebrick hat on) to confirm this.