Punkey/Bogey - remind me what you weigh? It's tricky when you're on the edge of the size range to determine what's going to be overkill and what's going to be just enough. I haven't ever experienced wheels that are too stiff, especially on a 29er. What happens when wheels are too stiff? Can the heavier spokes affect the natural ride characteristics of the carbon rims?
6'5" and 250lbs geared up. I'm not a wheel bashed but I do stress things out.
If your wheels are too heavy you'll just be making your bike feel sluggish. When spending this kind of dough you should be building durable but light. And we all know that 29ers need all the help they can get with rotational weight.
If your wheels are too stiff they can fatigue you prematurely and even more importantly they won't have that bit of give that helps them confront to the trail. Board stiff is generally not a good trait in frames, forks, wheels or bars.
I've also gotten info from two long term carbon rim manufacturers stating that they prefer to build with lighter spokes such as DT Revolution because it is easier on the spoke bed. I wouldn't use Revs except for an XC wheelset and I would stick with DT a Comps for burlier wheels.