The idea with this guide was to create a gaming PC without making any compromises in performance while staying within the budget of $2000. This means that I prioritized raw power over quality of life components.
I went with reference 980ti's because the (relatively) low price allows me to fit two within the budget, which provides a much bigger performance boost than a single factory overclocked card would. I honestly would have preferred Fury X's since they tend to outperform 980ti's in multiple GPU scenarios, but I couldn't fit two in without making big compromises in the build. They're apparently illegal in MSI's contest anyways.
The i5-6600k is more than enough for gaming and with an overclock can be pushed even further. A 5820k or 6700k wouldn't provide enough of a performance increase in games to warrant their much higher prices.
A good air cooler is better than a mediocre AIO cooler, which is why I went with the Noctua NH-D14, which perfectly in my budget.
I went with the cheapest motherboard I could to save cost, since this build is about maxing out performance for your money and a more expensive mobo would provide a negligible increase if any (you may be able to overclock slightly better).
16GB of RAM is arguable overkill, but some games are already coming close to maxing out 8 and people definitely can go over if they're doing other stuff in the background. For another $30 it's a no-brainer.
Samsung very reliable SSD's and I went with the biggest one I could within budget. It's big enough for your OS and a few AAA games.
750w is the perfect wattage for this build and this one is reliable, well reviewed, and cost effective.
Finally I went with a well sized case that looks good and will provide plenty of airflow for this build.
If you have any extra money I'd add some fans (I recommend Noctua) and more storage. A better CPU cooler would be nice but not really necessary.