Good on you for casting a level playing field. But unless I'm mistaken, the only company on this list having any model even close to a BK would be Woodstock Soapstone, and even then only one or two of their newer models, with regard to the OP's stated need for "low and slow". I think if you're in a contest for the lowest continuous output from a woodstove, a BK going to land the podium, every time.
That said, Woodstock makes great stoves, and is well-known for their excellent and reliable customer service. If you want soapstone, you would do well to consider them. If you want more classic iron or steel, then I'd venture to say BK is the only one I'd consider, for the stated goals.
As to size... I think some go too far in saying it doesn't matter at all. The implication is that, with a cat stove that can burn super low, the size of the stove really represents nothing more than the size of the fuel tank, with no relation to output power. This may be "more true" with a BK than with other stoves, but I still don't believe it's "absolutely true". I have an Ashford 30.1 in a small addition to my house (~1500 sq.ft.) with a lot of solar gain, and it's frankly too much on sunny days. You can try to build a smaller fire in a bigger stove, indeed I do this frequently, but there's a limit to that. You're not going to easily get the cat sufficiently heated to light off in a stove that big, on three small splits.
So, I'll buck the trend and say that, "yes a BK is what you want" for low and slow, but "maybe not the Princess" for a well-insulated 1200 sq,ft, in a mild climate. I'd be looking at the BK20's (Ashford, Chinook, Sirocco), NOT because they have a lower advertised output (they don't), but because I believe they'll be easier to operate with reliable cat light-off on the likely-desirable smaller loads of wood.
In evaluating this, remember that there's a roughly-fixed BTU value to each load of wood of given species and volume, consider it as a rough BTU/lb. constant. Also remember that in your climate, you likely often need some heat from that stove overnight, but do not want it putting out heat during the day. So, a stove that can be loaded with 3 cubic feet of wood, to put out constant heat for 30 hours, is completely useless to you. What you need is a stove that can do similarly low output overnight, but also loaded with a charge small enough to have it go out and cool off in the morning. Hence, the BK20, not 30 or Princess.
