If you're comparing the same size Ultra vs Horror, the specs are exactly the same (ww, nw, tw, ee, radius).
I personally think they turn exactly the same. The Horror does have Urban FK vs Freestyle FK of the Ultra but since you're a human and not a machine, its nothing you'd notice in turning.
The Horror is slightly mushier and easier to press but the Ultra is very easy to press as well. Not sure why you felt it was really stiff unless you were riding one that was too big for you.
The Horror is also a bit heavier. The Ultra has lighter core and the Horror has extra thick edges. Ultra also has a sintered base vs extruded.
Personally, I like them both and I think they ride exactly the same with the only difference being that the Horror is a hair flexier. If you trash your boards just get the Horror. (cheaper, beefier edges)
Thanks for the info. So, do you think the Ultra is as fun/playful as the Horror....but with construction upgrades that make it lighter/faster? Is the ultra really only a "hair" stiffer than the Horror? If you (or Nose) tell me that the Ultra is as playful (or close to as playful/fun/buttery/press-able) as the Horror....in a lighter package....I am sold for sure. Thanks again for the input.