How busy is the machine normally? If its not very busy it doesnt matter much. If it is a desktop, anything less than 19 will cause other things to slow down (I always had problems with netscape being INCREADIBLY slow when running seti). Try 10, if thats fine, try 0, if thats fine, try -5. If 0 isnt fine, try 9, then 8 then 7. Its time consuming, but it will help you figure out exactly what settings give you the best response and the best performance.