@TWhite 

If you are getting 160Mbps over the powerline link with P9, it means you have good speed and solid electric wiring.

Think of Deco P9 as "regular" Deco unit with integrated TP-Link powerline adapter. As such, what is applicable to TP-Link powerline adapters will be applicable to Deco P9 powerline link. I found TP-Link document that may be helpful for you: Explanation about the Powerline Rate and Actual speed of the Powerline Adapters

I would also recommend to review the following document: Most frequently asked questions about TP-Link powerline devices