My experience through level 44 has been that I solo heroic groups up to blue con slowly, but reliably. I am able to handily defeat solo encounters 5 levels above me. I've solo'd some green ^^^'s in long fights that completely depleted my power, but I guess if you're wanting to farm some named encounters, its doable. From what I can tell so far, the defiler is a formidable class and have enjoyed it a lot. Each level gets better and better =)