I'm not gonna be a lot of help here, since I haven't ridden a slayblade. I did go ahead and read up on it as if I were thinking about buying one myself though.
From the sounds of it this board is geared towards faster, aggressive riders. You said you ride the mountain, do a bit of jumping and tend to stay out of the park. This sounds more like a casual type of riding to me, but I could be wrong.
Also, from the videos I watched of people riding this board it looks stiff. At 135 you are definately a lighter person, and at 28 y/o i doubt your going to be going through a growth spurt in the next season or 2. So even a 153 probably isn't going to be very playful should you ever decide to broaden your riding to include jibs and buttering. Do I think you could ride a 153 and have a lot of fun? Yeah, the slayblade looks like an awesome board. Do I think it would be ideal based on what I know? Probably not, and this board is not cheap.
Like I said though, I haven't ridden this deck. If you could be a bit more specific in the type of riding you do that would help people who probably have some real experience with the board like Nivek, BA, Leo, etc help you out a lot more.
If nothing else consider this a bump so you can get some more views on this.