So no-one's got a gumwall tyre that skids predictably, apart from mantas' suggestion of the BLB Black Mamba. My experience of Paselas is that they're a bit too grippy, and jerky to skid.
I've been using Randonneurs on my one-braked fixed winter bike for ages and I really can't fault them on wear and skid control, just that they're a bit sluggish compared to a fancy roadie tyre.
This enquiry is for a fixieskidder I've been meaning to build.
I guess I'll forget the gumwall thing, and just go for rando, detonators or durano plus on the back, and something a bit less hardcore on the front.