RFM69 / 433MHz capacity

I've got 1 x RFM69 equipped EMONTX with 5 Second updates with another in the post, I also have an EMONTH and various 433MHz smart sockets controlled by an RFXCOM transceiver.

How close is this setup likely to take me to the available capacity in the 433MHz band? Should I think of cabling one of those EMONTX's direct?

Everything works OK with one EMONTX albeit I get an erroneous reading from one of the 3 connected temperature sensors from time to time.