Hi Kevin,
I've been a Mavic athlete for the past 8 years and I've recently become a Community Manager for them with all things related to MTB, so I'm kind of the Mavic answer guy now! Lol. You have a great question for me to cut my teeth on the MTBR.com message boards with. Manufactures continue to trickle down technologies and products keep getting better and better meanwhile the difference between their "best" and their "dream" products gets closer. Both wheels are great choices, they share a similar width and both rims utilize Fore drilling technology which means the inner wall doesn't have spoke holes. This process provides a stronger rim and makes them tubeless ready right out of the box. The biggest difference between these wheels is the materials used in the spoke. The Crosstrail utilizes a straight pull wire spoke and the Crossmax uses Zicral aluminum. The benefits of the Zicral spokes is the weight savings and it also makes the wheel feel stiffer. 80 grams of rotational weight is definitely significant, but its really up to you to decide if it's worth the investment. If you're the type of rider who needs to have the best or feels you can tell the difference between a Shimano XTR and an XT derailer you'll probably want the Crossmax ST, if you want to upgrade your current wheels and save a few bucks you won't be disappointed with the Crosstrail. I hope that info helps.