After all these years of use, the heating contractor who was installing my new oil boiler took one look at it and said its plumbed backwards! 
It's a double pass coil and I had the hot water going into the top of the coil. My heat exchanger is in the return so the hot water was in the half of the coil that "sees" the return air first. I have thermometers on the input and output sides of the coil and in general the forced air would knock the water temperature down by about 5 degrees. The heating contractor re-plumbed it and said I would probably see a modest increase in performance. Fast forward to now with the hot water entering the bottom half of the coil that "sees" the return air last. NOW it drops the water temp by 20-25 degrees. I think that's pretty amazing! Obviously the whole system works so much better. Moral of the story is I'm an idiot and double check your heat exchangers to see which way they are plumbed.
I was concerned this would knock the crap out of my Harman boiler and it would never recover. Ironically it will drop the temp to about 165 in the coal boiler and it will recover to 185 better than it did before. I guess its because the heat cycle demand is shorter. Full disclosure, it still struggles in extreme cold and wind. But for our normal winter weather it now works better than ever.
