300 Mbps is the maximum theoretical speed of wireless radio frames for the CPE510 if used with 40 MHz channel width (that is, two channels used simultaneously). Since the devices will negotiate best speed, they can fall back to 20 MHz channel at their will, so that speed for radio frames will be only 150 Mbps. Next limiting factor is AirTime. Since at any time only one device can send on a given channel, communication is half-duplex, therefore the devices get only a limited time-slice for sending data (that's called AirTime). So you can get 60 to 75 Mbps data rate with 20 MHz channel width at ~150 Mbps wireless rate in practice; but read on.

The CPE510 is designed for long-range distances in the kilometers range. 30 meters is like you are talking to a person standing next to you using a megaphone. You can try to lower signal power of the CPE510's and to use a fixed 802.11 mode (for example, 802.11n only) instead of mixed b/g/n mode in order to improve throughput. Also make sure both devices are exactly aligned to each other.

The ports are 100BASE-TX, so passive PoE is possible on the 4 unused wires of the cable. A 1000BASE-TX would require phantom powered PoE (802.3af), since all 8 wires must carry data also on a Gigabit port. This would significantly increase the costs for the device.