About CPU throttling, i'll agree with some that the high-end westmere parts are still up to the task, at least under windows. With the Titan X I get framerates almost identical to the ones published in GPU reviews, which are made on PCs equipped with the latest CPUs. You'll lose 3 fps there because of the CPU and one there because of the PCIe (and gain one back thanks to better memory bandwidth), but you get about 90-95% of the performance of a 2016 PC in most games, at least in 4K and I guess also in 1440p. Now in 1080p you might be CPU throttled so it's not the way to go if you're into 144fps gaming. There's still one game here or there that relies more heavily on the CPU where you'll see a performance gap though, but these are rarely fast paced/gorgeous graphics games so that's mostly OK. Most people don't have a 6700K and game developers tend to target the mid-performance tier in which our MPs are still competitive for now.
When it comes to OSX, I don't even see the point of talking about hardware performance in games. The framerate of any game is held back by the fact that every single piece of software involved in rendering the game (OS, driver, game) is poorly optimised, if at all, especially on recent nVidia GPUs. I gave up gaming on OSX a few years ago and now I don't get why would anyone serious about gaming want to play on OSX, let alone buy the latest high-end GPU to improve gaming performance on OSX when it's so easy to setup a windows partition. On windows, you benefit from decades of efforts tuning the software for gaming performance at every level for every hardware combination (well except for bad console ports, which is why some people hate consoles), which you won't ever have on OSX. OSX is OK for casual gaming, but casual gamers don't buy 1080s.
I'm looking forward to see some of you enjoy the 1080 in your MPs, I really hope NVidia will support these in their driver. I'll pass on this one though as I've lost too much money on the TX (which is still great by the way).