Currently...
I've currently taken apart my system so that my gaming is done on a single R6300v2 with bufferbloat control and the rest of my system is on the PEPLINK aggregating 3 DSL WANs. I have successfully managed to get 4 bridged modems -> 4 LEDE R6300v2 routers -> PEPLINK but, as mentioned above in several places this leads to very slow connects to web pages etc.
My current reading and experimentation is focused on Double Nats as mentioned by JMJones. I think that it may be that this problem may be exacerbated by 4 WANs on the PEPLINK.
Good references I have found on the internet include:
http://www.practicallynetworked.com/networking/fixing_double_nat.htm
This reference provides this advice:
The Remedy
To check for double NAT on your network, log into your router and look up the IP address of its WAN port. If you see an address in the 10.x.x.x or 192.168.x.x range (both of which are private) it means that the device your router's WAN port connects to is doing NAT, and hence, you're dealing with double NAT.
There are a several options available to correct -- or circumvent -- a double NAT situation. If the culprit is your ISP-supplied equipment, you may be able to access the device's configuration interface via a browser and set it up to work in "bridge" mode. This will disable NAT on the device and essentially make it transparent on the network so your router will receive the public IP address and perform the NAT function on its own. Instructions on how to activate bridge mode for your specific device can usually be found on the ISP's or device manufacturer's support site, but if you can't find the information or aren't comfortable making the change, an ISP's phone tech support will often do it for you on request (or at least walk you through it).
If, on the other hand, your double NAT is being caused by a third-party piece of equipment that needs to be connected in front of your router (the aforementioned VoIP adapters usually require/recommend this for quality-of-service reasons), eliminating double NAT really isn't an option-- but you can still get around it.
One way to compensate for double NAT is to set up separate port forwarding rules on each device so that incoming traffic is shepherded through both layers of NAT. So for example, on the first NAT device (the one closest to your Internet connection) forward the port(s) you need to the IP address of your router's WAN port. Then on your router, forward the same port(s) to the address of the device you need to reach.
If you have a lot of ports to forward, doing them individually can get a bit cumbersome, so a simpler method is to configure the first NAT device to make your router's IP address the DMZ. This will hustle all incoming traffic through the first layer of NAT no questions asked, but when it hits your router it will be filtered or forwarded as appropriate.
https://portforward.com/help/doublerouterportforwarding.htm
This reference provides similar ideas and a handy diagram:
The idea of the first reference seems practical and easy:
"If you have a lot of ports to forward, doing them individually can get a bit cumbersome, so a simpler method is to configure the first NAT device to make your router's IP address the DMZ. This will hustle all incoming traffic through the first layer of NAT no questions asked, but when it hits your router it will be filtered or forwarded as appropriate."
This makes particular sense with a LEDE router that functions only as a bufferbloat appliance.
So I am currently looking at this advice from LEDE
https://lede-project.org/docs/user-guide/firewall_configuration#simple_dmz_rule