[Note: although the linked apple document says the version number is “7.6.7” when I did the update the version number is “7.7.7” - this looks to be a typo on Apple’s documentation?]
After updating my Airport Extreme (6th generation) from firmware 7.7.3 to 7.7.7 I repeated earlier tests:
With 7.7.3:
On the main wifi network I can get full speed downloads/uploads (100/10)
On the Guest Wifi network routed through peplink using VLAN tagging, the download speed is terrible but the upload speed is normal : 0.6 / 10.
After updating to 7.7.7:
On the main wifi network I can get full speed downloads/uploads (100/10)
On the Guest Wifi network routed through peplink using VLAN tagging, I also get full speed (100/10).
Yay!
So it looks like 7.7.7 solves the issue we’ve been having.
Just FYI, the 7.6.7 code level refers to the Airport Express model, and the 7.7.7 code refers to the Airport Extreme. I will test this on an Airport Express to see if I get the same results.