Just an FYI...I recently used some extenders made by Veracity, which I got from ADI. The part numbers are VLS-1P-C and VLS-1P-B, their Long Range Ethernet and PoE Extender. I'm using it to power a Mobotix camera/keypad gate station which is on a run that's about 1000', no repeater or midpoint required.

The instructions even say that if you have four or more joins/couplers, "On site testing is recommended". I liked that part, since it seems like the guys who made the thing know that you don't always have optimal circumstances in the field.