I have connected 2 x VIGI C240 cameras to this NVR. I now want to add 2 more 4MP VIGI cameras but as the specifications say

1-ch @ 8MP, 2-ch @ 4MP, 4-ch @ 2MP

its a bit confusing as to whether the additional cameras will be able to record in the full 4MP resolution or do I have to reduce the resolution? I don't want to live view simultaneously all the cameras just record with all 4MP x 4 cameras, is it possible? What is the limiting factor with recording- bandwidth or megapixel or no of cameras? Can I record all 8 channels in 4MP if total b/w is within 80mbps?