Some black smoke is not a problem.
Check here
http://www.google.com/search?client=firefox-a&rls=org.mozilla%3Aen-US%3Aofficial&channel=s&hl=en&source=hp&q=turbo+wastegate+failure&btnG=Google+Search
Or you could mount a pressure gauge in the cabin. Full load between 0.7-0.8 bar.
http://www.asknumbers.com/bars-to-psi.aspx I understood 14 psi was okay, but maybe not, I get 11.6 maximum.
I wonder how many stock turbos have failed, in any fashion. I would think some, somewhere.