Looks nice and good move. I just changed from a dragon to new epa stove in my garage. I installed a new 8" triple wall through attic and out the roof with Selkirk single wall inside just a few years ago when a new roof was installed. The new stove is 6". I've just got it ran into a 8 to 6" reducer at the top of the stove right now which works ok.
I might put up some new 6" double wall above the stove, and then hook onto the 8" triple wall with an increaser at the ceiling. I might even add a section at the top like you have. Only bad thing is when you need to get up their and take your cap off, it could get hairy. We could always rig us up a wire brush on an angle with a telescoping rod for that.
I've got a Quadrafire Yosemite in my house which is the little brother to the IR. My old house is small at just about 900 square ft. and the Yose is nearly overkill at times but I do like it. I have no trouble getting long burn times plus the view of the fire and the looks of the stove and the way it sets on the hearth in my little place would be hard to match with another. If you get to thinking the IR would nearly be overkill, you might think about the Cumberland Gap, which is the middle of the road size. Good luck to you. If we didn't have some kind of new heating project in mind we might get bored.