King, that's an old Macro.. you never have to dismount anymore, it's automatic.
Soul: The only reason I can think of to use Rend is because of the arms talent 'Taste for Blood'. To use it for DPS without that talent is.. strange, to me at least. It does 182 damage (plus weapon dmg) over 21 sec.. that's 18 dmg per rage, ie. extremely inefficient. Let's say we max Rend with talents. We have 50% from Imp. Rend (two points wasted, if you ask me) and another 30% IF Trauma is up. So, that lands us at around 400 dmg, without factoring in weapon damage. With that... I'd say you'll have a max of 500 dmg (unless the additional damage benefits from Imp. Rend, in that case you'll have 600). So, you're looking at 50-60 DPR here. Now that Slam sustains your swing timer, rather than resets it, you'll get tons of more DPS just using that ability.
Rend has always been, and I fear will always be, a bad ability for DPS. It has some PvP utilities, and now some dmg utilities through talents (ie. 'Taste for Blood') but other than that, it's a waste of rage. Especially on higher levels. On really really low levels, it's efficient (like level 4...) but as you get higher it scales worse. And at 70 it's a DoT over 21 sec. What level 70 warrior takes 21 sec to kill his target? My main doesn't take that long, and he's prot!
Again, it's useless for DPS since it's weak and won't live through its uptime on higher levels.