More time is needed for observations.
Rather, pay attention to whether a cgminer has more or less rejected shares.
There are many factors that affect performance.
These indicators are never objective.
One comes out on the calculator in coinwarez, another is real obtained yields.
Exaple, if your bfg miner have 0 rejected shares for the perriod, however displayed 700 ks, the speed is 700 kh.
If cgminer have 2% rejected shares on similar period of time, however displayed 710 kh, the real speed is lower.
The pool will display 710 khs, but coins extractions is lower.
However note, that displayed speed in terminal is not the speed of the coins extraction
+-10khs does not matter
Just keep digging
