Theres no greater rush than racking along at 25-30 mph. No smoother ride either. Now a pace is something different. But even at higher speeds that pace will be smoother than at slow speeds.
For those that lean way back its more for looks. But when first learning to ride these big motor horses, its easier (its a mental thing) to feel safe and secure in your saddle if you put your feet way out front and lean back into the seat and cantle of your saddle.
Many will progress from this way of sitting the saddle to a more upright position but some never leave it. Its also a comfort thing.
Heres a cool video of some nice rackers and alot of pacers too. Many different riding styles demonstrated