I bought this year's Dark Series C2 BTX in February. Although, I have only had the chance to ride it five times - being a dual degree med student offers very little free time =/ - I really love the board. I'd classify my riding style to be the almost identical to your style. I spend about 80% of my time on the mountain and 20% in the park, unless I'm in the rockies where I search out as much powder as I can find and all mountain action. I was looking for a board that I could rip as fast as possible, while being stable. I also wanted the board to be playful, and capable of riding switch. Although, I do not spend much time in the park, I spend about 30% of the time riding switch and maybe more as I have progressed considerably. I also wanted this board to stand up to powder and backcountry, and something that I could grow into as I improved my freestyle ability this year. I would say that this board fit the bill very well, and I tell everyone that this board is more of a freerider's freestyling board.
Extremely fast and stable: Check.
In terms of speed, this board is downright ballistic, while being incredibly stable. Imagine a Hummer with the speed and agility of a Ferrari. Where I used to ride very cautiously on chop, I can now plow through with reckless abandon without fear of catching and edge. This is largely due to the stiffness (quite stiff at a 7.5 out of 10) and the added camber on tip and tail.
Playful: Yes, but not a jib stick.
Although the Dark Series is twin-directional with a half-inch set back, it feels just as good in switch as it does forward. Although it is very stiff, it is torsionally agile, and can spin well due to the banana between the legs. It has NASA grade pop. Fucking scary pop! I have been freeriding for several years, but have been forced to learn freestyle since I have been living in Philadelphia and all that is available are the park heavy Poconos. Therefore, I was not ready for the power of pop on this board, it does take much to get stratospheric. This board was made with riders who stomp massive jumps in mind. However, due to being incredibly stiff, it doesn't butter or press well at all. I can butter it, but it requires a tremendous amount of force and won't be as fun as buttering a softer board.
Carving ability: Depends on who you ask. Personally, I think it is great.
If you are a traditionalist, who loves big, long, soulful carves, this may not be for you. Although, I haven't had a problem with carving this board in any length or manner. The magnetraction is the real deal. Due to the thin waist and org throttle plates, this board is extremely nimble and accelerates perfectly in and out of turns.
Powder: Still haven't had the opportunity to really test it.
This board seems to work well in moderate powder of a foot, and maybe two. However, I am not sure how it performs in epic or backcountry pow. Though, I can tell you that Lib Tech Ripper Eric Jackson used this board when shooting "Black Winter" and he seemed to perform well on it in backcountry pow. You can find the webisode on Lib Tech's site or YouTube. You will notice he is using the 158, which has a blue and yellow base.
I am 5'11" 185 pounds and I bought the Dark Series in a 161. I have ridden for about 5 years and have always been partial to freeriding. I literally spent no time in the park up until this season. I didn't expect to get into park as much as I did this year, so sometimes I think that I may have bought the board a little too large. I wonder if I would have been better off with 158, for more all-mountain purposes. Although, if I wanted a board that I could learn park with I would have just bought a Skate Banana.
If anything, this board is meant for an advanced and aggressive freestyle-freerider who likes to catch massive air all over the mountain and go very fast. I would definitely suggest this board for you.