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Yes unfortunately I do, I have 9 rigs, 2 with 2 GPU's and the rest with only 1.
I know what efficiency means, was just wondering why it is so different for different people.
I have no idea what influences efficiency
Using mainly 5800's 2 6950's
I am using default settings, no overclocking, intensity 8
I am not worried about the Performance, was just wondering about the low efficiency
Ah they're not your computers?
No one would run an extra 120+W per card on purpose

Maybe work owns them?
A work request represents 2^32 hash attempts (without using rollntime)
For a good quality 6950 on default settings (e.g. GB HD 6950 900Mhz/775Mhz = ~365Mh/s) it should take about 11.77 seconds to complete the full 2^32 hash tests.
However, if it should get any LP messages during that 11.77 seconds then (by supposed definition) all the work requests queued and being worked on will be thrown away and give no more results than what has already been submitted - thus reducing your efficiency.
A higher intensity will make that worse also since it increases how long the GPU is working without replying.
A lower hash rate will also decrease efficiency for the same reason.
If the pool does merged mining and is sending non-BTC LP's (i.e. more than just a single BTC LP per network block) to you, it will reduce your efficiency that way.