what's the lowest wattage you managed to squeeze and maintain 50MHs on 1080ti ?

example:
rig 12x rog strix 1080TI, each set to 195W ~ 49-50MHs and doesnt seem to work any more efficient if I squeeze power limit below that. If I just touch the PL, hashrate drops to 46-48...

rig 6x msi gaming x 1080TI- 160W ~ 49 to 51MHs and works steady with 5454MHs mem clocks... power limit set to 200, actual usage 150-160... numbers measured on the wall seem to back up what nvidia-smi says. 

And I can't figure out what's causing such a huge difference... any ideas? I mean - I'm happy, but curious...

biostar tb250, xubuntu 16.04, 384.111, gpuclock offset set to +900, resulting in 5454MHz as reported by nvidia-smi --query-gpu=clocks.current.memory.