perhaps the potatoes are throttling due to poor air flow? try better cable management and a few delta 5000 rpm fans (be sure to strap the potatoes down 1st).
I don't have the report with me, but I believe it is actually cheaper to replace the potatoes after a day or two of mining. It really depends of the quality of the potato. When using high quality potatoes, the cost of the fans and extra electricity to run them could be justified. This is probably what most people would want to do as the price of cheaper potatoes is not that different from the high quality product. But, if you are like me and have a good supplier who can get you a good deal on bulk low grade product, it isn't really worth it.
