Xtina's belts are horrible. Her technique is all wrong (she doesn't know how to mix), and even in the studio you can hear her voice cracking and how throaty they are pretty much from D5 and above. She's honestly the most overrated singer today.
By comparison: http://www.youtube.com/watch?v=O4poK-jk2rE#t=2m12s
My girl Hojo would slay most of these broads, but I guess she's not the same generation.