It's hard to make a comparison without having either phone. Right now the 6P is my choice. I like the customization of the Moto XPE. The fingerprint reader and USB-C are some of the things that make me lean toward the 6P. I also like the look and build of the 6P a little better. If the Moto XPE had a fingerprint scanner and USB Type -c the choice would be a lot, lot harder.
I was a little confused about USB-C. My reasoning for liking it so much is because of my experience with my Chromebook Pixel. The ease of just plugging it in without fiddling with the connector is nice, and has a solid click when it's engaged. The other thing I like - and the part that confuses me some - is how fast the connector on my Pixel charges. It's just as fast, if not faster, than my Note 5 and Nexus 6 chargers, both of which utilize fast-charging. I once thought that having type-c automatically meant fast-charging and 3.0 but that's not the case. The Nexus 6P has USB-C and fast charging but is only 2.0
I don't really care that much about the faster data transfer, it was the fast-charging that impressed me.
The fingerprint scanner is the other thing I really like on the 6P. I'm not sure how good it will work but I have really gotten spoiled using it on my Note 5 and Iphone 6 Plus. I use mobile payments when I can, and really like it. I also like to use it with my password app, and app store purchases. Originally, the Iphone 6 Plus was the nicest and most convenient way to use all these features for me. Now that a Nexus phone will have these features I really like that.
Battery life I can't judge because I'd have to have both phones. If the Nexus 6P is as good as Google claims, that would be icing on the cake, and push me farther aways from the Moto XPE.
Also the fact that it's a Nexus and will have fast updates, and run the latest version of Android. this is not as big of a deal, since the Moto XPE is pretty close to stock and get's update pretty fast also.