Dell has posted the
data sheet of the forthcoming Axim X51. Nothing new here and it really looks exactly like the X50 (size, specs), except for power consumption where the X51 seems to use more at maximum CPU usage but less in sleep mode.
Meanwhile on a Chinese forum, someone posted
screenshots of the X51 running WM 5.0. At least to me they look very legit.
Thanks to Marquard!