So far, with my personal experiences on the bench, and with recomendations from other members here...the best plate configuration seems to be +nnn-nnn+, not sure of a numeric value for spacing, but I use only one washer between plates.
This configuration allows for the right ammount of electric in the cell as well as providing for a good ammount of surface areas where the HHO will be liberated.
A few factors that I have noticed for production without getting to hot is the volume of water(electrolyte), the ratio of water to material such as KOH, Salt, and others....and most of all...the ammount of electricity being drawn into the plates. All of that combined will affect your overall gas output and the ammount of heat you will have to work with.
There is an observation stated in another thread that with temp and amperage rise comes better production --- TO A LIMMIT --- After that limmit, you begin to take on an undesirable amount of heat and also spending more amperage while not getting any further efficiency in gas production.
"You don't always have to know ALL the answers, but you do need to know where to find them."