I don't think it would fit any more spacers, already quite a tight fit. Too bad, as I'd prefer a little more LOP, but it's fine as is. I keep the extra spacers and tools in the pack.
This one has quite a wide and grippy sling. I find it quite comfortable to wear, but I'm sure not everyone would feel the same. It also has a second strap that connects it to the side for more stability in the back position. It comes around your waist and clips into the sling.
If you're in Vancouver, you could try one on at Warriors & Wonders. They tend to have these in stock. The Grayman version I got looks less "tactical" than the other models, which I liked. The other colours have MOLLE on practically every surface possible.