The missing paste is on the cooler cold plate, i reckon there's enough paste and has just been a low/uneven pressure.
The paste wouldn't squeeze out round the edges if there wasn't enough.
Basically the cooler the 5800x the better. The AIO will see higher sustained boosts for longer and as for the fans it's hard to say but the difference will be negligable.
Try monitoring with the GPU-Z sensors tab or hwifo64, both software's should give more reading regarding temps, memory/vrm/hotspot etc.
Nevermind, i see afterburner beta includes these.
At that price you pay for bling mostly, the Arctic outperforms most and outperforms all at the same noise level. The EK AIO ran a tiny bit cooler but with higher noise/rpm.