If it was designed for a Z2 Lite, why not a Z2 Lite? The only thing being, a Z2 Lite was a kind of lime green colour that would be an 'interesting' contrast with the truly sublime Ibis paint job.
But if rigid is preferred, then even I wouldn't claim that any P2 short of a ti P2 is good enough for an Ibis, but what about a contemporary RC30/31? I believe they used to make them in 41cm length and IMO a Pace is good enough for an Ibis.