You are deciding between the case I have (V9 windowless side panel) and the case I want.
My vote goes to the PC-P50 as the cable management in that case is superior. The front fans are less blocked by the HDD bays. It has an extra 2mm of width - you certainly won't get the Mugen into the V9 with the top side fan installed. With side fans my GPU idle temps dropped 5C, the load temps stayed the same. It was my first build so I have a loud video card and stock AMD heatsink fan, all fan bays filled up and my system is not quiet. Maybe better choice in fans, aftermarket heatsink or a fan controller would help my system be quieter tho - I kind of doubt it - next time I build every component will have been chosen because it performs quietly.
You might wanna have a look at SPCR's recommended case list
if quiet is important to you.