As far as optical quality and durability i think you will like the Optika5 but its one butt ugly scope. Mounting surface area is also pretty small. Look for a MeoPro, there are still a few out there. Aside from cost the 2 big differences between the 5 and 6 are........The 5s are 1" and the 6s are 30mm. The Optika6 also weighs much more. You will get more MOA of adjustment out on the Optika6 also.
Overall the Optika5 comes in at a great price point with nice glass for the money. 1" will limit your choices a little for upper end rings. There are far more really nice 30mm rings out there.