What could cause two identical machines to display substantially different hash rates?
1) cgminer/Drivers/OS/Hardware are Identical
2) Temperatures are fine, and lower on the slower machine.
3) Machines are not overclocked or under-clocked
4) The machine with only two cards is running slower
Working:
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[P]ool management [G]PU management [S]ettings [D]isplay options [Q]uit
GPU 0: | 257.6M/210.0Mh/s | A:4 R:0 HW:0 U: 1.94/m I: 9
GPU 1: | 241.3M/209.1Mh/s | A:7 R:0 HW:0 U: 3.40/m I: 9
GPU 2: | 245.5M/211.0Mh/s | A:5 R:0 HW:0 U: 2.43/m I: 9
GPU 3: | 238.9M/209.7Mh/s | A:4 R:1 HW:0 U: 1.94/m I: 9
Broken:
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[P]ool management [G]PU management [S]ettings [D]isplay options [Q]uit
GPU 0: | 26.30M/42.08Mh/s | A:1 R:0 HW:0 U: 0.70/m I: 9
GPU 1: | 26.28M/42.67Mh/s | A:0 R:0 HW:0 U: 0.00/m I: 9
GPU 2: | 26.08M/42.47Mh/s | A:1 R:0 HW:0 U: 0.70/m I: 9
GPU 3: | 26.05M/38.76Mh/s | A:0 R:0 HW:0 U: 0.00/m I: 9