Fair review. I have had my xtr about 18-months (9,000 miles) and no problems - aside from the surging issues. Did you read the dodgy review in this weeks MCN comparing the F800gs against both the xtr and new z? Having just got back from a 2,500 mile tour of Scotland - I had to drive-up from the south coast of England on motorways (crusing at 80-plus with panniers and one lardy rider (17st) and pushed 100 from time to time to relieve the tedium - the review is a joke. The xt is written-off as having no grunt, excuss me, and not being up to serious touring.
I think, bearing in-mind the price difference between a new xtr and the xtz I would buy a z (the benefits of a double front disc, protection and apparent better fueling map) - its worth the extra few hundred pounds difference. Unfortunately for me the trade-in against my old xtr does not justify a swap at this point but if I were buying afresh it would.

Cheers,
Tomo