I think that's around 70 degrees, maybe a smidge higher. When I was trying to figure out which cams to get (2.8 is about 90 degrees) I stood in various spots where they were and held my arms at 90 or 70 degree angles so I could get a rough estimation of what it would be able to see.
Actually, I think I even got more serious. I found out what the field of view is on my iphone, took pics where the cameras would be, and then cropped out images from the iphone image so that I could see very precisely what the camera of various lens sizes would see.
I have two 2.8 on my exterior and one 4mm. I wish one of the 2.8 was a 4 but it was stupidly cheap at the time on ebay and I snatched it up. I think in general 4 is best for a driveway.