Does anybody have one [6940P] of these?

I haven't found many comments on them or end user reviews.

Does anyone have one of the SBR variants [6943P, 6944P, 6945P]?

Overall how do you like the Colt piston guns?

I know a few guys who have the 6940P, and it's a solid, accurate rifle. One of my friends runs his hard and has had zero reliability issues out of it.
Heavy barrel profile under the handguards. Chunkier than the 6940, but well balanced.

I own 2 DI 6940's but would like to have a 6940P in the safe too.

there are some around that were manufactured for agencies
over runs have been offered for sale
GB has an upper for sale currently

Colt has made both 10.3 inch and a 14.5 inch versions of their 5.56 piston carbine. There's a complete 10.3 inch upper for sale on G.B. right now.
The Colt website shows the 10.3 inch (SCW0921P) and 14.5 inch (P0923) models for sale to Law Enforcement:
http://www.colt.com/Catalog/LawEnforcement/Products/ColtAdvancedPistonSystem.aspx#9685-features--models
I've not yet seen the 14.5 inch upper offered for sale to civilians yet, however.
I have the 16 inch version (6940P), and I like it a lot. Shoots as well for me as any of my D.I. rifles and carbines, and it's a lot easier to clean.