To answer your question, the load lifters are barely useful. Load lifters are not the most important part of a pack (to me) or I would just get another pack (being cheap also plays a part in my not getting another pack). I really like the other parts of the pack, though (great hip belt, simple lightweight design, etc.).
I can't seem to find the article I remember, but this is a great one that describes load lifters: http://www.backpackinglight.com/cgi-bin/backpackinglight/how_packs_work.html#.UZT760qNN8E
Under Part 1, look for the paragraph that starts with "Load lifters should be here discussed". The picture looks a lot like your pack on you (or my pack on me). The description is pretty much spot on, in my opinion. The load lifters are helpful, but just barely.
I wish I could find the other article, since it shows what a good load lifter system looks like. As mentioned, 45 degrees is ideal.
Long story short, I would definitely consider another pack, just so you can get the load lifter angle right. You could size up, but as mentioned, the pack probably wouldn't fit you very well if you did that. The fact that Granite Gear is often mentioned when it comes to load lifter problems suggests that they have flaws in their design (or had flaws in their design). This is a shame, since it is otherwise a great pack. Even with that flaw, lots of people have been really happy with their packs (it used to be a very common pack for thru hikers -- now it has probably been replaced by ULA packs).