Steve, i've driven my GTI 12500 miles mate and can tell you on any roads it rules. Are you referring to motorways with MW? If so that's exactly where the GTD will shine and it is a great great car for what it is. My mate getting one is a rep so it's perfect.
AND you are right, in some areas the GTD WILL be better than a GTI, for you it is and that's all that matters.