One thing to keep in mind is that if your provider uses PPPoE, it is quite CPU-heavy. Moreover the netgraph-based PPPoE implementation that pfsense/opnsense use

One thing to keep in mind is that if your provider uses PPPoE, it is quite CPU-heavy. Moreover the netgraph-based PPPoE implementation that pfsense/opnsense uses is single-threaded. So if you have a multi-gig connection, you need a CPU with very good single-thread performance. Linux has a multi-threaded implementation, so it's probably less of an issue on OpenWrt. Interestingly, some ARM SoCs that are worse on paper do much better because they hardware-accelerate PPPoE (e.g. recent MediaTek Filogic SoCs or some Qualcomm/Marvel SoCs). Most of those routers also use less power and have great WiFi. The downside (coming back to buffer bloat) is that they may not be able to do multi-gbit SQM.