EX6150-100UKS FastLane and Ethernet connection issue

FastLane dedicates a radio (ideally the 5 Ghz band) as a backhaul connection to the router.  If your extender isn't getting a solid connection at 5G, then you either need to use it on the 2.4 ghz band or not use it at all.  Also, in a dual-band extender like the EX6150, you might find that your 5 ghz devices get better performance if you use the basic mode.  The net here is that it's worth trying out a couple of options, and then settle on the one that works best in your particular situation.

The ethernet performance should always be higher than the wifi performance, because ethernet is faster than the extender's wifi network.  But the difference often isn't that large (especially when the backhaul wifi link to the router is the bottleneck).  What speeds are you seeing, and how does they compare with using the extender wifi?