Apple has fixed 802.11ac SMB transfer speeds with the release of OS X Mavericks.
Back in June, it was discovered that the new MacBook Air’s 802.11ac Wi-Fi performance was being artificially limited by OS X. Apple was not dynamically scaling the TCP window size.
With the release of OS X Mountain Lion 10.8.5, Apple fixed the issue for AFP file transfers over 802.11ac; however, the problem still remained for SMB transfers.
Ars reports that now the issue is resolved for SMB file transfers as well:
We installed OS X 10.9.0 on both a 2013 MacBook Air and our file server and re-ran the same tests one more time….
Two big takeaways here: first, AFP transfer speeds have improved even more since 10.8.5, on the order of about 21 percent. Second, SMB transfer speeds have finally been fixed—these numbers show a 137 percent increase, well over double the transfer speeds that were possible before. SMB is now on par with AFP speeds.
via Ars Technica