I had hoped the brown pair (Pins 7/8) would be clear of any use by these devices, so that I could purloin them for some other operation.
According to the link Jeallen has provided, only gigabit ethernet operation would have these enabled, unless I am reading the chart incorrectly.
@Channel Hopper
Not sure that is correct - the paragraph on the linked page starting "Standards-based..." states this:
"Standards-based Power over Ethernet is implemented following the specifications in IEEE 802.3af-2003. A phantom power technique is used to allow the powered pairs to also carry data.
This permits its use not only with 10BASE-T and 100BASE-TX, which use only two of the four pairs in the cable, but also with
1000BASE-T (gigabit Ethernet), which uses all four pairs for data transmission. This is possible because all versions of Ethernet over twisted pair cable specify differential data transmission over each pair with transformer coupling; the DC supply and load connections can be made to the transformer center-taps at each end. Each pair thus operates in common mode as one side of the DC supply, so two pairs are required to complete the circuit. The polarity of the DC supply may be inverted by crossover MDI-X cables; the powered device must operate with either pair: spare pairs 4–5 and 7–8 or data pairs 1–2 and 3–6. Polarity is required on data pairs, and ambiguously implemented for spare pairs, with the use of a diode bridge. "
Therefore you could use a 100Mbs ethernet connection, and that would leave two of the four pairs free for your intended application.
Ref your original connection about the Wifi extenders: if you connected a 10M/100M ONLY network switch, and a not a GB one, to the router, then anything on the "far side" of that switch, including the extender unit would be operating in a 10M/100M circuit environment, and thus, you could presumably treat the latter as outlined in the quoted para above. You would need to find a 10M/100M PoE switch, but, IIRC, I think they are available s/h on ebay etc.
That description would also appear to allow you to "do almost whatever you want" in terms of DC connections to the secondaries of 2 pairs of the coupling transformers if you wanted to try "something different".
Interesting "aside" ref my CCTV system for which you fitted my cameras: the HiLook NVR has a "self adaptive 10/100/1000 Mbps network interface", whereas the cameras themselves have only a "10M/100M self adaptive" ethernet interface.
