Toward the end of last carpet season, I experimented with Spool vs Gear Diff (with 500k traxxas oil) in both a TC6.1 and a Schui Mi4 on medium to high grip carpet.

What I found with both cars was that the Gear diff dove into corners a bit more, and was smoother through the corner. With the spool, corner exit traction was much, much better. I prefered the feel of the gear diff, and could drive it more consistently, but the spool was still faster because of the corner exit traction and our tight/technical track layout. Playing around with front droop made it easier to drive, and I eventually got used to it.

This season I'm only running the Schui (sold the TC6 because I wasn't any faster with it, and it was worth more ), but I have added the DCJ front driveshafts. IMO, it's the best of both worlds. You get the corner exit traction of the spool, but it's much smoother and feels more like a gear diff into and through the corner. So I'm quite happy with them.

-Mike