Season 6 of the show is fantastic, you need to watch it no matter what!
After that you could watch about 10 episodes total in seasons 7 and 8 and get the point.
Ark of Truth is a horrible piece of garbage, but if you watch seasons 9 and 10 it's the conclusion. Contimuum is just a sand off thing that goes through the history of the franchise. But both I wouldn't watch unless you are familiar with the last two seasons.