there Welcome to the Forum.
The fueling probs you mention seem to be able to be sorted out with various mods etc. My Xtx has the markings to suggest it was the worst type of ECU ending 00 but it seems fine to me. All the later models seem better! Anyway there's loads of very easy adjustment threads on this forum.
The Xt is much longer legged bike than the DRZ and I certainly can maintain 75mph to 80mph on motorways and fast A roads no problem, and I still get about 55-60mpg at those speeds.
Hope this helps you make the right choice.
