As said on the corsair web page for the 400c the maximum gpu length is 370mm, and im not sure whether if the 370mm is measured with or without the front case fan. If it was measured without the front case fans, the push/pull radiator mounted on the front set up would be 75mm(2x corsair sp 25mm fans, 1x240mm radiator), leaving only 295mm for the gpu. The strix 1080 is measured 298mm, so im not sure if that extra 3mm would cause any problems?