This is similar to a recent change in iwm, but it only affects 11n mode in this driver.
The condition being removed below was added by me before the RTS threshold was enabled in net80211. So now we should not need it anymore and removing it might actually improve things by removing RTS overhead for small frames. Please test. Index: if_iwn.c =================================================================== RCS file: /cvs/src/sys/dev/pci/if_iwn.c,v retrieving revision 1.174 diff -u -p -r1.174 if_iwn.c --- if_iwn.c 8 Oct 2016 14:44:36 -0000 1.174 +++ if_iwn.c 24 Oct 2016 09:13:36 -0000 @@ -2959,8 +2959,6 @@ iwn_tx(struct iwn_softc *sc, struct mbuf else if (ic->ic_protmode == IEEE80211_PROT_RTSCTS) flags |= IWN_TX_NEED_RTS; } - else if (ni->ni_flags & IEEE80211_NODE_HT) - flags |= IWN_TX_NEED_RTS; if (flags & (IWN_TX_NEED_RTS | IWN_TX_NEED_CTS)) { if (sc->hw_type != IWN_HW_REV_TYPE_4965) {