I've been operating at a continuous of about 700-1000 all year, with or without the damper. Damper helps to a degree bring things down, but I feel like small adjustments now are often much bigger than before. I generally can't even get a good solid flame held without keeping the door cracked until the flue is around 600 degrees using quality firewood measured with an MC.
I feel like I'm still losing a ton out the chimney, but not nearly as much. Flames are lazy now and lick slowly most of the time. These high temps are still achievable with the damper for me. Maybe I can close the damper more than I am currently, but the one time I closed it a little too much, I started to smell the faint whiff of smoke coming from the stove. I couldn't determine the location where it was coming from and couldn't see it, but since then, haven't closed it over about 50-60%.
There'll be times where I can close the air off to 0% and have the damper closed 60% and be cruising at 800 in the flue, then other times I've got the damper closed 25% and the air at 50% with the same results on a different similarly sized load. MC of the wood is all around 16%.
Anything over 20% goes into next years piles and I've been pretty particular about that. I don't check every piece, but I multiple batch check every tree that I can.
I saw a post not long ago in the SBI forum about my particular stove that another owner was having a similar issue and hated the Osburn 3500 compared to his old 2000. He had to add a damper and modify his air intake to even get it to perform close to the old 2000. I considered PMing him and asking him what kind of modification he did, but I'm not sure I want to go that route. The damper is good enough for me I think -- I don't understand the operation of the stove well enough to feel confident in modifying the air intake.
The stove did me pretty good all winter, albeit it being a fairly mild one here. 95% of the winter I wasn't using propane with the main room being 70-80 and the coldest room of the house being 60-70. I wouldn't give it a 5/5 stars by any means (3/5 initially) but the damper bumps it up to at least a 3.5 or 4 out of 5.