@bonnecomm:
Would the system be expected to work better if I deleted OPT1-OPT6?
Are you using the OPT interfaces to log into the modems? If you're not using them at all then you may as well delete them, but I don't see why it would help anything if your speeds are slow. I have a similar setup and it works fine.
In my experience, if you have speed issues with MLPPP then it usually comes down to one of
-a low DSL sync rate on one or more modem
-packet loss on one or more modem
-mtu/mru/mrru misconfiguration
Also in my experience, you're likely to get more help troubleshooting MLPPP issues in forums where there are more MLPPP users, such as the Teksavvy forum on dslreports.com. That's where you'll get more help with the troubleshooting and concepts, then you come back here if necessary for details on implementation (although there are plenty of pfsense and freebsd mlppp users in the other forums too).