Usually people are looking to use a EPA ZC as their primary heat. When that is the case, if money isn't an issue, I would always go bigger. 3000 sq ft is quite a bit. You may have an issue getting even heat upstairs. However, with the cat, you should be able to achieve secondary burn without stuffing it to the gills. I always figure I would rather have excess firebox and not need it.
On the other hand, if you are truly going to be a casual burner as it seems, I might go with the smaller stove and save the $.
On the other hand, if you are truly going to be a casual burner as it seems, I might go with the smaller stove and save the $.