Encryption for IOT devices with minimal overhead
For passively powered RFID tags, I settled on 160-bit ECC (Curve25519) to exchange the keys and SPECK for the actual encryption on a software platform.  If I make my own hardware, I use SIMON instead of SPECK.  For an IoT application, I see no reason not to do something similar.

If you are looking for comparisons of symmetric ciphers regarding throughput and power, I would suggest the SIMON and SPECK paper and the paper on PRESENT as both have good power tables and comparisons.