I should have pointed out that's all you could get. Back in the day, they made a 12.5 PV and I used a bunch of them.
So, I'll say 3-4 inches lower than cruise if you can get the PV, if not it is a 10.5 because that's what you can get.
Example B might have 13 inches of cruise vacuum so a 10.5 would work. Next up would be an 8.5 because I don't think they make a 9.5 PV. It's all about getting the PV as close as you can to cruise vacuum so it opens at the right time. If your cruising at 16 inches and have a 4.5 PV the engine will think it's waiting all day for the extra load fuel.
