Mmm difficult one, I'd hate to put you off an XT, everyones expectations and experience are different. People have done serious milage two-up on all the XT's. But personally I"d only take a pillion for a short blast on my XTX, no way i would consider a serious trip with a passenger, not enough power, seat comfort or space. But that's just me and my personal exprience of the XTX.
Good luck, let us know!
Selina