I have 3 Antminer S9's each with the Bitmain AP3++ PSU running on an APC 7863 PDU.  This PDU has 21 NEMA L5-20R 120v receptacles (normal household-looking American 120V outlets) and 6 NEMA L6-20 208v receptacles.  It has an L21-20p male plug connected to a 3-phase 20 amp circuit in a commercial building. 

Currently, each miner is plugged into a separate leg on the PDU using the standard L5 120V connectors.  Each L5 connector indicates its respective power leg to make it easy to balance the load.  One S9 is in an L1 labeled outlet, one in an L2, and the last one in an L3.  Each leg is reporting ~12amps on the PDU's LED display and the miners are getting about 13.6TH/s. 

My question is whether or not it would be of any benefit to use the beefier L6-20 connectors instead of the L5 connectors.  The L6 connectors are labeled "L1-L2," "L2-L3," and "L3-L1."  The output voltage of these connectors is 208v. 

Would I get any efficiency gains buy using three 208V outlets vs three 120v outlets?  I believe the amps/leg would stay the same.  Is it dangerous to use the 208V connections for 3 antminers in terms of power balance (ie. one miner shuts off and then L1-L2 and L2-L3 have miners, but L3-L1 doesn't... and vice versa)?  I am a total n00b as far as 3-phase power is concerned and this is my first foray into using it. 

I believe:

current setup: One S9 on each 120v leg (L1, L2, L3)
                     1400w / 120v = ~11.67amps per line

Contemplated setup: One S9 on each 208V line pair (L1-L2, L2-L3, L3-L1)
                               1400w / 208v = ~6.73amps per line pair
                               6.7 ÷ √(3)  = 3.89 amps at 3-phase
                               3.89 x 3 = 11.67amps per line

Questions:
Would there be any benefit to using the 208v plugs?  Is there any danger to using the 208v plugs in my setup?

Any help is appreciated, thanks!