That is almost the build I am aiming for.
That i7 4790k sounds really good and relatively overclockable by Intel standards, so you could have fun/tragedy with that and your custom CPU cooler
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The R9 390 is quite pricey but if you can afford it (not sure I can) then I reckon it is a solid buy. You might want to aim for a lower price point if you aren't gaming over 1080p though it will certainly last you for a while before you need to upgrade.
Motherboard looks good though I haven't really researched that one.
Are you getting a single slot of 8GB RAM? It is usually much better to get matching pairs.
That build should be quite a powerhouse, it looks like you should be able to do some 4K gaming though you won't be getting to Ultra settings in any games and still keep a decent FPS. It gets my thumbs up for a very solid gaming PC by the looks of it.
Edit: Someone just pointed out on my thread that the i7 CPUs aren't really needed for gaming so you might want to consider a good i5 instead if that is your only concern.
You might want a more powerful PSU as well, the 390 draws 250W of power I think, so that is half gone right there, I'm sure you'd be well within limits but you might want some more wiggle room for future upgrades or whatnot.