Rested XP is % of level. I've been told you max at 2 "free" levels worth. This XP didn't get counted with quest XP although it DOES work with daily dungeon finder stuff. It shows up as +50% XP for you, which stacks with the 50% from armory chest, any XP from scrolls for crafting/gathering and bonus XP from making/gathering quality products.

so all that.. it is really hard to say exactly how much you'll get from it.