The rims are really too wide for 23's, I'd say 25's probably, and definitely 28's. I run 28's on my A719's, no problem. Mavic lists 28's as the narrowest to be used with them. Keep in mind, actual tire widths vary between brands, models, etc.

P.S. Are you aware the XT rear hub has 135mm axle spacing? Modern road bikes have 130mm rear dropout spacing.