What type of devices for the AP and client? What is the distance between them? What are the WiFi settings? Are they aligned to each other, do they have free line of sight?

Without basic information of your setup it's impossible to give any tip for increasing the bandwidth.

CPE210s are 300mbps devices as in 300/8=37.5MB/s (airtime) which in actual real life translates to not more than 15-20MB/sec given specific best-case conditions. What's more the ethernet port on the switch is 100mbps, which in turn translates to 12.5MB/sec...if you factor in the half-duplex inefficiency of the medium, you'd be lucky to achieve more than 7-10MB/sec in full-duplex speed, i.e. 56-80mbps using this gear....which seems about what you are indeed getting ;)

On a sidenote if you believe than in the 100ft apart there's more headroom to play with than what you are getting try reducing (yes reducing) the Tx power in both the AP and the CL and give it another go. :)

You can set 802.11n-only WiFi mode rather than 802.11b/g/n mixed mode and up to 40 MHz channel width (20/40 mixed is the actual setting if I remember correctly). This saves AirTime, gives better signal strength and therefore increases throughput somewhat. Also make sure to align the CPEs exactly to each other and to set the distance setting to the real distance (should be 0.3km or Auto mode for 100ft).

Max. bandwidth for CPE210 in an ideal setup is ~95 Mbps full-duplex (limited only by the WiFi bandwidth of 300 Mbps half-duplex; this is the high mark for a N300 device even if it would have a Gigabit Ethernet interface), while actual throughput depends on many factors such as latency etc. 50 Mbps throughput is a good result in 2.4 Ghz band already, but in a sparse populated area you should be able to increase this even further.