If using Hikvision camera, I would use the Hikvision NVR such as the 7716NI-I4/16P. but your Hikvison camera is 4MP, and the 7716NI-I4/16P incoming bandwidth is only 160Mbps. So you are probably some how limited by the bandwidth.
I like the Dahua NVR as some of the model they have with built...