The current preview window is functional but there are some drawbacks, mainly with respect to scale and weapons being cutoff on the ends.
My suggestion is that there be a button on the preview window that when checked, allows your character to actually wear the armor as shown in the preview window for a limited period of time (10 seconds). During this time you would have complete control over your character. After 10 seconds your character would revert back to his/her regular self.
This way you can see what the gear actually looks like on your character during actual game play as opposed to a zoomed in window. The difference between the two can sometimes be night and day.