This was discussed on another page a couple days ago, with an individual claiming he burned a fraction of the wood by doubling up a pump that was already overkill in singular form. The fact is, that your building(s) require X amount of BTU. Your stove needs to burn X amount of wood to make that BTU. The flow rate to get it there will have no bearing on the amount of BTU used because the heat load remains the same regardless of flow. Now, if you have low return temps, your burn cycles may be longer, but considering your exchange rate is slower, it balances out. I have a hard time believing 5GPM is accomplished through 230ft of 1" with that little pump, but I'm not doing the math either. Seems to me that pump should push around 3.5-4 on that loop. A larger pump like a 26-99 or even the large Badger or Liquidus if you want a cheap one, should bring you back up to the 7 range and keep your return temps up. As was mentioned above, the 20 degree design temp is kind of a wive's tale. As long as return temps stay above 140, there is no problem. However, there is some merit in that it takes less wood to keep 200 gallons of water at 160 vs 180. So if you can keep your supply temps low to save on a little wood, a tight delta T is necessary to keep return temps above condensation. If you need to run 200 degree water, you can have a 55 degree delta and the boiler won't care. It's all about keeping return temps up