muleman,
I have an EKO 60 with 500 gal. However, I have an exceptionally large heat load, with two homes, one of them being a large converted barn, half of which has 13' ceilings, plus several thousand square feet of attached building that we used to have our business in. So except in warmer weather, such as 25F+, I am using much of the heat that is produced. Based on average wood consumption I have been tracking since October, I am averaging an output of 50K BTU/hr in Oct, up to 80K BTU/hr through December. So my heat storage capacity of about 83K BTU for the 500 gal tank will carry me only about an hour or two at best in the coldest weather. The boiler and storage are in the basement, so there is very little wasted heat. Given that situation, I pretty much run the EKO 24/7. I have found this works the best, and I maintain a deep bed of coals. When I let the fire run out, it takes half a day to really get everything back up to temp, and a good hot bed of coals built up again.
In answer to your direct question, burning like that, I find I need to refuel pretty much every 4-6 hours. Much longer than that, and I have used up most of the embers, and have to start the climb back up again. So I need to run mine more like a conventional wood furnace, in terms of feeding it wood. In my situation, even 2,000 gal of storage would only give me 4-6 hours of heat, which would help me extend heat between burns, but I would have to relight the fire each time. I have found it easier to just keep the fire going more or less continuously, even if I feed it smaller loads of wood. It still gasifies beautifully though, and as long as I have the coals, I get a clean blue flame, so I am getting the efficiency. We just have a dogonne big structure though, and it uses a lot of BTU's. We are on track to come in at burning 10-11 full cords of wood for this winter. Sounds like a lot of wood, but it replaces a lot of oil as well! We have used only a few gallons of oil so far, and only when I was too lazy to keep the beast fed properly, and decided to let the oil burners run overnight.