I came to the 6P from the N5. I adapted to the bigger size in no time, it still fits in a shirt pocket and you can still hold it with one hand (if barely). The 2K Amoled screen is much much better than a 1080P LED screen, the colors are bright and vibrant and the text is super sharp. Amoled also has a wider field of view than a LED screen which is something you notice when you have the phone dash mounted as a GPS, with the old N5 I could see the screen because it was tilted toward me but my girlfriend couldn't see it from the passenger seat, with the 6P she can see it too, it was something she remarked on immediately. I showed the phone to a few of my friends at dinner last night, the iPhone users remarked on how sharp it was, of course the resolution of a iPhone6S is very poor even compared to the 5X, but coming from the 5 it was something I noticed also but not so much as the enhanced colors.
The processor in the 6P is faster than the 5X but I don't think this makes a difference because I found the performance of my 5, which is slightly slower than the 5X, to be very satisfactory. The cameras are pretty much the same on both. The 6P can have more storage than the 5X. I got the 64G 6P but truth be told I never had a problem with the 32G limitation on the 5 or my previous phone the Galaxy Nexus, however at only $50 I said what the hell and got the extra storage. The bottom line is it's the screen that sells the 6P.
The price difference isn't that great so unless you are very cost constrained there is no question that the 6P is the better choice.