Baraka_Guru

Well, you might as well finish BC first. If you aren't level 68 or higher, there's no point in buying WotLK yet. Just as well, getting Cataclysm won't make sense either, as it's generally for level 80 to 85. You will have access to some new stuff, but not the new areas.

If I were you, I'd hold off until you have a character who is actually ready to use the new material.

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Knowing that death is certain and that the time of death is uncertain, what's the most important thing?
—Bhikkhuni Pema Chödrön

Humankind cannot bear very much reality.
—From "Burnt Norton," Four Quartets (1936), T. S. Eliot