[Nexus 6P Q&A, Help & Troubleshooting] cb474:
Unfortunately, I really don't think that is a good assumption. You really should read ArsTechnica's analysis of the 810 and its problems, if you haven't already. http://arstechnica.com/gadgets/2015/04/in-depth-with-the-snapdragon-810s-heat-problems/

They show that once the 810 warms up and starts throttling, it underperforms older chipsets, like the 805 and 801. So I think there is a very good possibility that the Nexus 6P will be slower than quite a few other phones, even older ones.

Also it's not accurate that all flagships out there, other than Samsung, have gone with the 810. Several have opted for the 808 instead, which is technically a lesser chipset, but doesn't have the overheating and throttling issues, so actually has a CPU that performs better. The LG G4 and their upcoming V10 both use the 808. Reviews seem to indicate that it was a smart choice. The new 3rd Gen Moto X Pure edition also uses the 808. That's really a pretty good choice if you want close to a pure Android experience. It's the closest option, probably to the 6P. I'd probably get one instead of the 6P if it would work with T-Mobile's wifi calling. Oh, and of course, the Nexus 5X uses the 808, so even Google has hedged their bets on the wisdom of using the 810 chipset.

So there are other choices.

Keep in mind, as I've said in earlier posts, that a chipset is not just the CPU. It incluces the GPU, the radios for wifi and cellular, other elements that I believe influence camera performance, and more. So companies like Google aren't choosing the 810 because, despite its flaws with the CPU, it's the best option out there for a flagship CPU. This is clearly not the case. The CPU is inferior in many instances (depending on how you use the phone) to older CPUs. Rather, they're choosing the 810 because its the most advanced and up to date Qualcomm chipset in other respects. So they're putting up with the CPU to get other things (for example, the Nexus 5X can't do the 240 fps slow motion video that the 6P can do, because of elements in the chipset other than the CPU). Whether or not this is a wise decision is debateable since the 810 has caused a lot of problems in other phones (stuttering, overheating, lags, spontanous shutdowns).

If you're concerned you really should wait for reviews, especially by good sites like ArsTechnica that know how to properly test the CPU. It is entirely possible that the 6P won't have overheating issues, but will throttle and have performance no better than and even not as good as the one year old Nexus 6 (which uses the 805 that has already been shown to outperform the 810 once it starts throttling). It is also entirely possible that the Nexus 5X, even though it does not have all the bells and whistles of the 6P, will offer a smoother and less laggy experience that the Nexus 6P. With the better CPU in the 808, plus a lower resolution screen, that's definitely a combination more likely to result in a smooth experience.

So, you know, I'd keep my expectations low and not assume the Nexus 6P with throttling will be better than other phones out their with the 808 or 805 chipsets. It may be fine. And it may be more or less on a par, depending a lot on how you use it, with most other flagship devices. But assuming that it's "going to be smoother and less laggy than all other devices in the market" I think is very likely not to be true.