BK will probably be easier for you to use at your current level- they generate a bunch of Fury for you, which makes life easier. Later on, if you are pushing GRs, Istvans are better for that.
Zodiac will be better for you than CoE (I should have mentioned this before). Another thing you can try, which should get you more damage and toughness too, is to craft the Guardian’s set. This set is particularly good for low-paragon players like yourself.
To implement that, you’ll need two out of 3 pieces of the Guardian’s set- for you, it will ideally be the helm and bracer.
You’ll equip the Guardian’s Helm and Bracer, plus 5 pieces of the Wastes set (Shoulder, Glove, Chest, Pants, Boots). You will wear Zodiac + RoRG. In the cube you will have BoM. Or you could also wear the BoM, but make sure the affix roll is close to 80%. A BoM can roll as low as 60%, which gives only half as much toughness!
Then, swap Mantle of Channeling in the cube for Mortick’s Brace. This should help you both to be tougher, and do more damage.
Finally, just let me just clarify what Ring of Royal Grandeur does: it reduces the number of pieces needed for a set bonus by 1. So you can get a 6-piece bonus with only 5 pieces equipped (like with Wastes) or a 3 piece bonus with only 2 pieces equipped (like with Aughild, Crimson, or Guardian). But, bear in mind that it only works with sets with at least 3 pieces (so you can’t use just one of the BK swords and get the bonus).
So, generally this ring is used to combine different sets together, in this case Wastes and Guardian’s. If you are just using 6 pieces of one set, and that’s it, you don’t need RoRG.