I use J cradles with my 2 Malibu xFactors and they work okay. Made 4 trips to Central Oregon with no problems. That being said, on two occassions I have broken 2 of the plastic cradle bases while driving in high winds (40-50 mph), but Thule has replaced them free of charge. Always make sure to securely tie down the bows of both kayaks to two locations to minimize torque on the cradles. I think an xfactor is bigger than an outback so you shouldn't have any issues as long as everything is tied down securely.
Also, I bought my cradles in 2000. I think the new designs are stronger.
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