I haven't cast the new Xi2, but my XP is an excellent rod. A cuple of months ago, I fished in Belize, and we fished with eights most of the time and nines when the wind picked up(we were fishing for permit exclusively). The XP ten would be good if you were fishing with heavier flies. For the small tarpon in the river, an eight would be fine.
As for the problem with you eight weight. What kind of rod is it? What kind of line?
One cast can change your day...maybe your life.