I have a stock 16mm bar and bushings for sale too, if more than one person is interested in this upgrade. I will ship it in the box that my 19mm bar came in. PM me if interested.
It is my opinion that a RSB won't increase ride harshness, regardless of what size you install. I'm sure the stock 16mm bar would provide a huge handling improvement over having no bar at all. The 19mm bar provides even flatter handling. It's my guess that a 22mm bar would convert the car too much toward oversteer for my tastes (especially when the roads are wet/slippery), but this is just a guess as I've never driven the car with a 22mm bar installed.