Well actually, the salt recommendation are very much different and not many domestic units recommend higher than 3500 ppm. Most Australian units recommend between 4000 - 6000 ppm. The reason is mostly in the power supply design than direct effects on the cell.
PPH, if you still have problems with your system, you can e-mail me directly, I can most likely help you with this (I hired the most knowledgable person on AutoClear in the industry!).
sassam@teamhorner.com