I'm not replying to anything specific in this post, but am providing my experience to add to the pool of data.
I've got original turbos with 94K miles and GD supersplit downpipes, as well as testpipes. I have no smoke and have been running this setup for ~5K miles. I do have an HKS Sport cat-back, which is a baffled design for NAs but still flows better than stock so my exhaust is not completely open.