[asid61]

Colson wheels are unbeatable.
We tried that green tread above, blue nitrile, assorted wedgetop, roughtop, pneumatic, higrip, banebots orange, and delrin (we have a lot of tread and wheels).
Of those, I would rank colson as waaaay above anything else, followed by banebots, trailed by pneumatics. Everything else was iffy. We didn't have great results with the green tread, but perhaps it's not the same stuff.

Polycord also gets pretty decent grip.