I'd be curious to hear your pros and cons after having both...
TBH, I ordered both knowing one was going back. I didn't know which one but figured I would be able to decide before the return period was up. The 6P arrived first as I was quite excited to try "pure" android and my first Nexus. I liked it a lot, the speakers, the nice screen, but was kinda big, although probably could have gotten used to it size wise. After a week I decide to order the MXPE. It arrived in 3 days, wow, fast delivery. First time I held it I knew this was scoring big points over the 6P already just for the feel in hand. The backside was nice and grippy. It was a stock back and dark blue, but grippy. This is the first time in ages I felt I could go case less. Even the 6P was to slick to safely hold for me. Then I notice quickly on my first call that an annoyance I had with the 6P was missing on the MXPE. So comfortable to hold. The dimple on the backside is perfect for placing a finger in as you hold it to your ear. The size of the 6P slab wore out my hand and I'd find myself switching hands a lot. I do have smaller hands tho and perhaps anyone with bigger hands wouldn't find this a problem. it was a nice feature tho, that dimple.
Other observations: the speakers on both sounded great, however, the MXPE wins imo for deeper richer sound. Both phones are good but I give the edge on speaker sound to the MXPE.
When standing them up side by side the MXPE is a little shorter in height. Same screen size yet shorter, another plus imo and made it more easily pocket-able.
Both on my wifi, side by side speed test was an absolute wash out, same/same. So close not an issue either way.
Again the feel of the MXPE in hand was winning me over as I place a lot of weight in comfort.
Updates, the 6P wins. The MXPE is sorely lagging in the security updates. I think I got one, maybe two is all. Not that big a deal to me tho so wasn't much of an issue.
YMMV, but when it comes down to it for me after using the 6P for a about 10 days I knew the choice had been made soon after I put my sim in the MXPE and started setting it up. The 6P lost big points for it's blah slab appearance, the less comfy in hand feel on especially longer calls. The fact I felt it needed a case for slips, the slightly larger size. The MXPE won big for the choices of backside options and over all great feel in hand.
Another MXPE plus is it can be set to light up the lock screen when close enough to be looking at it. A nice feature at first then I set it to light up when I picked it up instead. I liked that a lot better.
It runs very light as far as bloat, just the Moto apps which are fine and some convenient.
The MXPE is quite inexpensive these days, not sure about the 6P pricing.
in any case , I'm starting to ramble. IMHO the MXPE edges out the 6P but not by a wide margin, kinda depends on what's important to each individual, and this has been my 2cents. Good luck