I am not 100% sure about the stairmaster. But the sierrascope is an upgraded Horror. The sierra comes with carbon fiber reinforcements (like the indoor), a sinter base and keeps the shape of the Horror. I personally ride a Horror and my friend got a sierra. I have rode both and you really cant go wrong with either one. They are just fun sticks to shred the mountain with.
My boyfriend has a sierrascope and he loves it. Hes been boardin for about 20 years and has had a whole bunch of boards. He had a battalion too with the TBT. But he likes his sierrascope. His bindings are too big for me so i havent rode it yet cause we havent switched bindigs just yet....but I strapped on at the bottom of the mountain as best as I could and the board definiely felt pretty sweet...the flex was cool. And you can butter with those things like.....butter....lol....the reverse camber is pretty nice also
Anyway, the sierrascope is just a better version of the horrorscope. Sierra took the best part of the horrorscope and added an even better base.
I know the sierrascope is on sale for a crazy good price now on sierrasnowboard.com. I was even contemplating getting one...but Im too busy spending money on snowboarding trips lol
Tested mine out one this week and it is sweet. Capita definitely nailed it with the flat kick reverse camber, its more suttle than other rockers so if you're making that transition from regular camber it's not super extreme.
Though if you're looking wanting regular camber then just shoot for the stair master. For something that's a little stiffer, more stable at high speeds, and has more pop the Sierrascope would be the way to go.