The overhead of gigabit ethernet is 6% so efficiency is 94% with standard 1518 byte frames.
WiFi is much more complicated than it seems because its advertised peak modulation schemes such as 3/4 256-QAM barely work under the best of conditions so are likely to fall back to slower ones in normal use >10' away. The signal strength required goes up with both wider bands (e.g. 160MHz wide) and bonding more antennas (2x2, 3x3) so you are even less likely to connect at full speed. Any interference at all will result in lost packets and retransmits. Furthermore, while AC takes less airtime to send the data, preambles, ACK packets, RTS, CTS and the CSMA protocol take just as long as before for backward compatibility so while N had...