My answer to the same question (actually, replacing a 155 Jett, but I'd been through a 155 Lithia earlier) was the SI Turbomatic Gel Flow. It's just a bit narrower, so if you fall somewhere between Spec's 155 and 143, it might be worth a try. I much prefer the shape of the cut-out, too, though unfortunately the padding has seemed to compress very quickly.
There's always Brooks, if the weight isn't an issue for you. I've speculated here before that a monocoque saddle with a rear much wider than the nose can't be extremely T-shaped, because something has to support the "wings."
Speed comes from what you put behind you. - Judi Ketteler