Jay, I don't think it's either of those . Can't imagine that a 12 valve head will flow better then a 24valve head (which is also newer in design ) up top, also Ed (RBYCC) doesn't seem to have problems with his boost control which leads me to believe that there is some issue in the wastegate. First thing that I'll check is if it opens fully, problem is that it's below the turbo and the spring/lock washer is hard to get off .

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190E 3.0-24v (M104 980) turbo @ 0.8 bar
1/4 mile: 2.483 / 13.540 / 175.17 km/h (street tires)