The P2 (platinum) is Superflower, and the GQ (gold) is FPS, that's correct. That being said, both are quality PSUs.
You don't 'need' 1000W, but for the same price, assuming you want sizeable OC headroom and want to continue with power hungry cards, the 1000W GQ sounds like a pretty good deal to me. You'd be using the 850W at ~76% on very rare occasions, if ever (max draw, no OCing). You'd be using the GQ in the ~65% range under the same circumstances. Unlikely to actually impact longevity, but the GQ would be under less stress (although, 'real world', unlikely to be an issue either way).