Hi @DanMesh,

Welcome!  Indeed I have many posts on this (most in 2020).  So you're saying two total EAP245V3's?  One ethernet connected and one MESH?

That is a little different from my MESH setup, I have two Ethernet-connected EAP245V's and two MESH-connected EAP225-Outdoors (one per Root Node).

MESH is implemented using the 5GHz Wifi radio only.  What I have observed for my setup, as a very rough rule of thumb, is there is roughly a 50% reduction in real throughput for each wireless hop based on the air link rate of said hop.

So, for example:

1) 2x2 Wifi5 client (iPhone XSM) connected to EAP245V3 directly.  Air link rate 866 MBit/sec.  Actual throughput ~350-500 Mbit/sec

2) 2x2 Wifi5 client (EAP225-Outdoor) connected to EAP245V3 directly -- ethernet connected speed test PC connected to EAP225-OD for testing.  Actual throughput ~350-500 Mbit/sec

3) 2x2 Wifi5 client (iPhone XSM) connected to EAP225-OD via Wifi, which is in turn, MESHED to EAP245V3.  (aka 2 hops).   Actual throughput ~110-170 Mbit/sec

Or in other words, if all air links were negotiated at 866 Mbit/sec, two hops would give you a maximum theoretical throughput of, at most, 1/4 of the link rate:

866 * 0.5 * 0.5 = 216 Mbit/sec (I've seen up to ~170 Mbit/sec max with mine).

Now your case is somewhat different from mine.  Because EAP245V3 to EAP245V3 via MESH is a 4x4 scenario -- Aka AC1750.  I'm not sure I've ever seen anyone bench test this.  Theoretically, it should be better than what I am seeing.

Your MESH backhaul real throughput should be roughly 867 Mbit/sec (assuming a pristine airlink of ~1734).  So devices connected via Ethernet to the second AP should see speeds up to this speed.  Wireless clients connected to the second AP should see about half that -- or roughly 433 Mbit/sec.

Good luck!  Keep us posted,

Jonathan