I was in the area in mid july 2016. When planning the trip, I was hesitating between 864 or 862. But I could not get an accurate idea to chose the best road. Though, we visited Detifoss waterfall by the 862. Once there, we've asked a 4 wheels Icelandic driver what to do. He did not recommend to keep driving by the 862 until Asbyrgi. But on the point when the road split up to the north, we've crossed a Hyundai i30 going down south. I've asked, and the US driver told me that although the road was unpaved, it could be done perfectly if driving carefully. So, we did it instead listening the locals advice.
If the road does not get into worse conditions, my advice is that it can be done with a normal car (we're traveling with a VW California Camper).
In order to help other people, I've uploaded this short video on the section where we found some puddles.
In fact, at the end of the video you can see an approaching motorhome doing the same road.
Regards from Spain.
