tware

I have a problem deciding which camera to buy or what to do. I have a nuuo drv card running 7 cameras on a pc. In the back of the property, I have a 700 tvl camera, but when someone come on property at nite I cannot see there face. The camera is setup on top of the building covering 60 to 70 ft. IR lights the area very well but the video is too grainly to tell who it is. Do anyone have a suggestion to help with my problem.