I'll start; 15" +/-.

But the most important thing to figure out right from the start is whether you cruise on the idle circuit or on the main circuit. That, even more than the cruise vacuum, will be the most important factor.

If it cruises on the main circuit, you will have a much easier time dialing in the low speed transitions. But if it cruises on the idle circuit, you will have a bunch of compromises to hash out.

Most of mine end up cruising on the idle circuit. Which means I need the PV to open early, so I usually have a 10.5 PV.