Tomringler,
The carbon buildup problem you speak of in the ecoboost is due to driver error. These engines are like the new diesels as far build. They are purposely built to work. So when you drive them on short trips with a soft foot, carbon will build like said before in any engine. Boosted engines see the effects more drastically than NA. So every now and then take it on the freeway and drop the hammer on the on ramp, this will blow all the carbon build up out of the tail pipes. One more thing, lower octane levels mean increased carbon in the powertrain, lesson I learned the hard way. These engines may say they can run on 85 minimum, but I wouldn't run it consistently on that octane. I have an 07 Navi with the 5.4 and when I bought it the tailpipe was black inside which means the previous owner ran the lower grade of fuel. I only run 91+, which is about $5 difference between 85 and 91 per fill up. My tailpipe is clean inside, no knocking from the engine, oil comes out caramel at 5K miles instead of black (full synthetic), and when I tickle the skinny pedal the engines sings me a sweet melody at 91 octane. I would not hesitate to get the ecoboost, I would just open the throttle once a week to make sure there is no junk in the engine.
Sorry for the long post, but hope this helps.
