anuyunn

Depends what you need, i would pick HS50 from these two ( just because the Stinger looks ridiculous and has shit earpads ). 
If you're after sound quality and position pinpoint accuracy, none of them - get Superlux 668B or Samson SR850 or if your budget lets the Philips SHP9500 ( best from all of mentioned ). 

HS50 and Stinger is "Bottom-End" headphones or like someone would say "trash", while the 668B, SR850 and SHP9500 is Low-End ( Entry Audiophile ) and is comparable to all other 50-200$ headphones.

Basically all 120mm and 140mm AIOs are crap, and so are most of the <$100 MasterLiquids made by CM for that matter. Money is better spent on a decent air cooler.

Yes, you can easily run it with a 500w psu, but what's your budget for your gpu? 

Wattage is not relevant.
Quality/spec of the PSU you use is relevant.
 
With 500W I assume you mean such garbage as the EVGA 500B, do you?
If so, pls replace it. 450W is enough, but you need a good quality one like Bitfenix Formula, Whisper M, be quiet Straight Power 11. Or Cougar GX-F (550W)

the wattage they recommend is just there for users with crap power supplies, the 580 doesn't need that kind of wattage.

I run my RX 580 RedDragon V2 with the BeQuiet System Power 9 400W. Works perfectly fine.

Yeah, should be fine, as long as it has the right connectors

580 has a faster GPU, so despite having less ram, it should perform faster in most titles. Are you targeting 1080p 60fps?

1080p --> RX 580 4GB
1440p or higher --> RX 570 8GB is better, but consider something a tier faster than the RX 580 instead.
 
Extra VRAM does help, bu not that noticeable with a mid range GPU like these.
 
OC or not doesnt matter, it only refers to factory overclocking. You can overclock yourself on both models if you'd like to.

well then there ya have it

Then Either case would be suitable enough to cool your system adequately,. The Nexus M has enough ventilation to meet the heat demand, so if you prefer the look of it, go that route. 
 
My rule of thumb is it's okay to get aesthetically pleasing cases as long as they can adequately provide airflow to the system you're building. Anyone who tells you "Airflow or bust" is full of hot air  

Go for the nexus m.

PSU shroud and clean lines FTMFW, I still say the Nexus IMHO.