Hum, I think the car if everything is running okay, tests alright et al... should be fed a diet of Heavy Duty Engine Oil.... perhaps some HI milage on the thick side ???
Shoot, after changing to a heavy weight for a couple OCI's if that don't take care of it, then I'd reason with a couple cans of RESTORE. Used it before with some (several results) in favor of it (real world experience).
But first, is always to go heavier IMO.
I would if it were mine, even think on adding a few ounces of a thickener to a standard oil to use up what you already may have. So for instance, if you have several OCI's of a thinner weight, buy one bottle of the thickener. Don't throw good money after bad.
BUt in the short of it. It may be excessive IYO, and it can be better, but it's not the end of the world, and your car if everything checks out could last an additional 100000 or more maybe much more with it burning that bad.
Changing oil does matter. Some cars just don't like certain brands.
I've had oil burners before, many in fact and you'd be surprised how far they will go, continual to the drop of what they do burn. Just watch out if consumption INCREASES from here on out.
If you want to do a oil test go ahead if you have the extra dough, but then keep in mind it takes a series of them to even have a clue of what is normal. Be prepared to count the costs if money is tight, and if not, then do what you fell like.
Just for my information, how much soot is collected in the tailpipe and is it very ashy or is it tacky?