are these (as well as the CorkSport version) made of carbon steel or at least 400 series stainless ?

 

First off both companies offer some well built and quality products and I have used and have them on my MAZDA. I also know many of the people at both companies and often speak with them!
Both companies have GREAT customer service

Both companies use an already existing muffler for their offered exhaust products and contract out to another company to have the product manufactured for them with their specifications. As for content both use stainless steel. I couldn't tell'ya if it is 400 regarding all the component's that make up the completed unit. Not many companies in the aftermarket do btw! And actually I don't know of any!
Just an FYI the water that comes from your exhaust during those cold morning start up is normal (unless a engine or cooling system problem) but the water is highly corrosive to all metals if you are not allowing the engine to completely get to all the operating temperatures and allow the exhaust system to burn off the exhaust water. This generally takes on average about 15 minutes of driving. Less then that the water will slowly deteriorate the exhaust system piping and eventually you will start to see holes in your exhaust system from the CAT back.