After using a Pixel 7 for the past twelve months, I would only ever want to use the largest available Pixel model partly so that I can have as much screen surface area as possible and partly to address Google's choice of height to width ratio. To give credit where credit is due, I think Apple's iPhones, for my needs, have the ideal screen ratio.
How this pertains to this discussion about the P9 series is that early information (below) says that the P9 Pro XL will be smaller than the P8 Pro.
I was planning to use the P7 for two or three years before upgrading. But based on this, I might buy the P8 Pro once the P9 series is launched.
https://9to5google.com/2024/01/23/pixel-9-pro-leak-render/
"The OnLeaks x MySmartPrice piece says the Pixel 9 Pro will have a 6.5-inch display that would be notably smaller than the 6.7-inch panel on the 8 Pro."