Cure for analysis paralysis - biggest, highest quality, stove you can afford, install an OAK, buy quality pellets, sit back, grab a favorite beverage and enjoy the heat.
XXV to me was a piece of furniture with a payback. I enjoy having it around, even in the summer.
Based on your description/layout, I would say no less than 50k BTU to be safe, not sorry. Unlike a traditional wood stove, going too big on a pellet stove only results in a small potential loss of efficiency, but gives you plenty of headroom for really cold nights.
My husband is reading all the posts and picking up on the xxv ones. Which is fine, I want it too. It just feels like a splurge for style (which does matter, of course) when we don't have any money for splurging. if only there was a p series with ~50k btus...then I would have one priced in the mid of p43 and p61a and it would be easier.
That XXV is much prettier though...