They're unique, so you can only have one, they don't stack. Bear tartare was nerfed to be basically wasteful. Use any spare runes/flasks you have and just fly through it. It only took me about 12 hours post-exp nerf. It's really not a large leveling experience this time. Mostly likely because they don't do anything but make you weaker as you level. Your stats go down relatively as you level and your lose legendary perks halfway through, so if they drew it out longer it would just completely suck.