I have a PPPoA ISP, my Draytek 120 is connected to pfSense in bridge mode, no issues, no lag, no problem. That modem, once you choose PPPoE<->PPPoA passthrough disables NAT and Firewall, also DHCP is disabled….a dumb modem.
My pfSense unit takes care of what it can do better than a 25 euro combo modem/router.
In the past I had a half-bridge configuration, using a Netgear WNDR3700 router (running openWRT, arokh builds) coupled to a Digicom Modem (it supported half bridge), pfSense seems not to support half-bridge scenarios.
Just my experience, ADSL 20/1.