Air France indeed goes out of T2. Since AF and Saudia are Sky Team partners you should be able to check through and get your international boarding pass when you check in for your domestic flight. And they should take care of you if you miss connections. But that won't be much comfort if you really have to be in the UK on that day.

I have found Saudia to be mostly on time but every now and then they've been an hour or two late. Also, a number of the domestic arrivals at RUH are bused in rather than using a loading bridge. That can add another 10 minutes or so to your transfer time.

If you want maximum peace of mind you'll want to go for the 5-hour connection. The only thing is RUH is a dull dull dull place to hang around for long. If you're in business and you have lounge access that might help. Saudia was building a new international lounge but I'm not sure if it's done yet.

It's a tricky call but I would lean toward the longer connection.