Personally I stretch my inventory so it's in a 4x4 layout, I've always liked it like that. One thing i'd suggest is swapping the prayer interface with the ranged one so you don't have to look as far away from what you were killing to activate/toggle your prayers. I like how you put the defensive abilities section to the very far side, it's pretty useless having it open at all unless you do any kind of tanking at PvM especially when you have the main defensive abilities already on your action bar

It's your interface though, do with it whatever you want lol