Though I do not have a 6P, my advice to you is to buy it now.
Yes, new Nexus devices are coming, but the 6P is an amazing handset and if you don't want to pay top flagship dollar for a Nexus phone (and who knows, maybe when this new Nexus device comes out, you may like the 6P better, or it may, subjectively, not be as good as the 6P in some respects), the 6P has been out for a while, and so it won't hurt your wallet as much.
Of course, if you do want the 6P but want to pay even less, you can always wait until the new Nexus device comes out and grab the 6P; because then it would have dropped in price even more by that point.
Either way, this is a decision only you can make. I'm like you - I hate waiting for phones! But sometimes by waiting for a little while, you get the phone at a decent price; or you wait even longer and get it at a super good deal.
And even if you buy the 6P and the new Nexus comes out, it's not like you're suddenly stuck with a not-so-good device. I have a feeling that the 6P will be relevant for a long time. Do what you feel is best for you.
Let us know what you decide!
Posted via the Android Central App