My fatbottom 4x12 straight is 14" deep, just like my Bogner 4x12. Are you sure yours is 17" ? Maybe they changed it ?I use the FB's. They are deeper than most cabs (I think 17" total), but short. They are sealed back, and less leaky than screw back cabs or some other sealed back cabs.
Due to this, they are more directional as someone pointed out.
The do have tight low end, with a nice amount of low end resonance. The stock speakers are fairly tight, slightly dark, but I like them. They are in the Eminence Wizard tone territory, but they are not Wizards and do sound different. I do not know if VHT is shipping their new speaker yet, but those should be good too.