Old AC66u, first time connecting to AC, is IPv6 needed?

We upgraded the Intel N-6230 card to their AC-7260 card. In the "Network and Sharing Center" the connection "Speed" rises to 390Mbps, sometimes lower, sometimes higher. The old card never went above 260Mbps. We are trying to only use 5Ghz cus the router is very close to our work area.


However, at speedtest.net our connection speed has now dropped from always being at 60-65Mbps to only...

Old AC66u, first time connecting to AC, is IPv6 needed?