I have both Spinergys (Xyclone Disc) and Mavics (Crossmax ST and old Crossmax SL). I'm about 200-220lb geared up and am moderately aggressive as well.
First, let me clear something up. Spinergy spokes are easy to find. Just call Spinergy and they'll have them in the mail to you ASAP. $5 for a single spoke is the price I paid. They sent two extras when I ordered two. There's only one spoke length for the entire wheel set too, so keeping extras is _much_ easier. I've never had to use a replacement spoke.
Spinergys
What I like:
-Light
-Durable
-Robust freehub (Hadley made)
-Strong
-32 Spoke Design
What I dislike:
-17mm internal rim
-Not true UST (but I did set them up with Tubeless Ready tires and Cafe Latex)
-If using with tubeless tape (above) truing becomes problematic, but I've only trued them once
Mavics
What I like (I have lighter models than what you're considering):
-Weight (for a true UST system)
-Durable
-19mm internal rim width
What I dislike:
-24 hole design (although they've held up, no problems)
-Freehub design is inferior
-Customer service is *rumored* to be terrible
Bottom Line
Duncan had good advice regarding weight. I'll add a little to that.
If you're worried about longevity go Spinergy, the freehub design and 32 über strong spokes stand up to a lot of abuse. They're durable as all hell.
If you want to run true 2.35in+ tires (Nevegal sized) go Mavic. If you want to go true UST go Mavic as well, no muss no fuss.
You didn't ask, but I'd also look into sending a Lefty front hub to
Universal Cycles as well. You can have them build you up a nice set of 819s with a Shimano XT 775 (if you're a loose ball fan) or Hope (if you like cart. bearings and have a bit more $) rear hub. You'll get an über durable wheel for less $ (Shimano rear) that has easy tubeless setup but weighs a bit more. I went this route for my SS and am happy with the cost, durability, easy tubeless setup and easy/cheap maintenance.
