Single slot AIOs are meant for ITX builds where there's not enough CPU cooler clearance for proper CPU cooler. But for PC cases where you have enough CPU cooler clearance, most air coolers will outperform single slot AIOs. For AIOs to be effective, you're looking towards at least 240mm rad, preferably 280mm or 360mm rad.
Phanteks P400S has CPU cooler clearance of 160mm and you can put any mid-sized CPU cooler into it, e.g Arctic Freezer i32 (150mm tall) that is also cooling my i5-6600K in my Skylake build with 2x Corsair ML120 Pro fans in push-pull configuration (full specs with pics in my sig).
specs:
https://www.arctic.ac/eu_en/freezer-i32.html
review:
http://www.tomshardware.com/reviews/arctic-freezer-i32-cooler,5004.html
pcpp:
https://pcpartpicker.com/product/rz7CmG/arctic-cooling-cpu-cooler-acfre00004a
You can also pick any other CPU air cooler from this list, just make sure the overall height is under 160mm,
link: http://www.tomshardware.com/reviews/best-cpu-coolers,4181.html