Quite interesting tour, but following must be taken into account:
You must demand all 8 hours, as 6 will not be enough. Everything depends on Cairo traffic, which can be worse than traffic in UK.
At Egyptian Museum, the Mummies exhibition is the MUST, very interesting but requires at least one extra hour and additional ticket at extra cost.
You probably want to spend as little time as possible at the Mosque, as there isn't that much to see there.
The most interesting part of the tour was the market, so much to see... Loved the antiques shops that you will find quite a few. I would say minimum 2 hours or more needed at he Khan el-Khalili.
I wouldn't go with lunch option as this counted as part of your tour, and takes another 1.5 hours or so of your sightseeing, if possible grab yourself a sandwich there will be plenty of time to eat whilst in the car in between viewpoints.
Otherwise thumbs up for Viator, quite efficient and organized.