I've used the Cusco Tarmac center diff to alter the bias % F/R from 50/50 to 65/35. It was nice, and on a roadcourse, would be close to ideal. For my needs, it showed a weakness in the lack of limiting wheelspin. If the rear wheels broke loose, they would continue to spin until I pedalled the throttle and costing time. In the wet it was worse for times, but stupid fun.
I've since installed a spec-UK DCCD unit paired with a DCCDPro controller. The maps programmed into the controller exceeded my expectations in every way. That would be my reccomendation to anyone wanting to maximize the AWD platform.