First, I have never taken this route. I know this from a friend. UP highways are decent and wider but passing through cities will slow you down. After Chandauli take Mohania- Sasaram- Bikramganj- Ara- Bihta instead of Mohania- Ara direct which is shortest but not good.
PS. If you're on a road trip this a good road but if your sole purpose is to reach Patna and faster then i'd advise against it.