Honestly I don't see the point of AIOs at all, they sit awkwardly between high end air coolers and a proper custom loop. Sure, they're convenient, but they're only slightly better than a proper air cooler yet cost more, are louder and more prone to failure.
AIOs make sense in compact setups where there's no space for an air cooler, otherwise I'd steer clear. I regret buying into this fad.
Also, what, why would he go from r9 390 to a GTX 1060? They,re really close in performance, sure the GTX is more power efficient but that's about it. Similarly, why would he swap NH-U12S to a 120mm AIO? Even in cooling power that's a sidegrade.
For editing the Ivy Bridge i5 is showing its age, I'd personally save up until Ryzen upgrade (either 6 core or even 8 core) is feasible, and sell the ivy CPU/DDR/Mobo. A 2600 would cool well under that Noctua, be night and day in video editing and provide a slight boost in gaming. That would also be a platform you could build on in the future.
Example:
https://uk.pcpartpicker.com/list/z82vbX at £388, would result in a respectable gaming/editing setup especially for 1080p. I don't know how much a 3570k/8gig/Z77 would sell for, maybe £140 is in the ballpark? Either way, you could easily fit a case in that budget as well, after selling the old hardware.