Out of all current model Porsche 911 (i.e. 2005+ 997 series) on the road, how many are TURBO?
The figures from Porsche are not quite specific enough, but if you look over the historical data and figure that in, you can probably make a rough estimate.
From 2005-2007, Porsche sold a little over 36000 Carrera models in the US. With another model year since that, and the US accounting for nearly half of Porsche's market, there are porbably around 100000 997s that have been produced by the factory since it was introduced.
Looking at known numbers for past Turbo Carreras, these have normally accounted for almost 10% of the production total. However, the turbo version was not introduced until 2006... so there are probably about 7500 total world wide out of the 100000 Carreras out there.