I use a Netgear R6700 running DD-WRT. The 5G band supports only AC, and my MBP is the only device using 5G. Sometimes it connects at MCS 7 and achieves 867 mbps. Other times it connects at MCS 9 and achieves 878 mbps. While the speeds are similar (and I'm not complaining), MCS 7 is using 3 spatial streams, but MCS 9 is using only two. I see the same RSSI and SNR at both MCS. Any thoughts on why it goes back and forth? Thanks for your help.