Here are some test results on the grandpa of them all... Linksys WRT54G v2.0, alive and kicking since year 2003, lucky one with 32MB RAM from factory
NAT speed, iperf with gigabit wired workstations on both sides:
1) OpenWRT 10.03.1 pushes ~27 Mbit/s, thats the last usable OpenWRT on these beasts, things went to drain after that
2) LEDE stable 17.01.2 branch, ~18 Mbit/s, I guess we can "thank" kernel developers for removing kernel cache, and adding general bloat every year
3) LEDE stable + @dissent1 PR applied makes it to ~32 Mbit/s, using fast_classifier/shortcut_fe combo. Looks promising, may give a second life to this box!
Btw, tested shortcut-fe-cm, no effect at all.
Also, is it necessary to hardcode IPV6 dependency for building these modules? Wastes precious 4MB flash