That would have to be some insanely weak hardware for pfSense to have a problem, considering most routers are an order of magnitude slower still and handle it fine. PPP doesn't even register as consuming any CPU on my box.
USER PID %CPU %MEM VSZ RSS TT STAT STARTED TIME COMMAND
root 4828 0.0 0.2 14456 6712 - Ss 7Dec20 0:32.58 /usr/local/sbin/mpd5 -b -k -d /var/etc -f mpd_opt8.conf -p /var/run/pppoe_opt8.pid -s ppp pppoeclient
root 8216 0.0 0.1 6904 2480 - Is 17:27 0:00.07 /usr/local/bin/dpinger -S -r 0 -i WAN_ZEN_DHCP6 -B fe80::1%pppoe0 -p /var/run/dpinger_WAN_ZEN_DHCP6~fe80::1%pppoe0~fe80::4afd:8eff:feaa:a4d1%pppoe0.pid -u /var/run/dpinger_WAN_ZEN_DHCP6~fe80::1%pppoe0
root 76224 0.0 0.2 14456 8900 - Ss 17:15 0:00.03 /usr/local/sbin/mpd5 -b -k -d /var/etc -f mpd_wan.conf -p /var/run/pppoe_wan.pid -s ppp pppoeclient
I'm only marginally concerned mine might struggle on Gigabit
I don't understand what the NIC queues is about though, so I'll give you that. But I'm only seeing people mentioning that as an issue at Gigabit speeds, so I should hopefully be able to see if that's an issue later this year.