Hey mate, I gather you're young, & I don't know your circumstances wrt financial commitments etc.
My gut feeling would be to go for it, because if it really is in the powerpoint presentation industry that you've always dreamt about & you don't take it, you'll wake up at 40 or 50 something and wonder "what if", speaking from experience.
I understand you're in line for a promotion, and that's great, but if it isn't what you're passionate about in the long term, is it worth staying there &passing up a chance at something you dream of doing? Generally, if you're passionate about something you'll excel at it (in your case, Microsoft excel).
I'd see staying where you are as like an Asian dessert - safe, but ultimately dull and insipid; whereas the other opportunity is like a degustation meal at a fine restaurant (western of course) - you don't exactly know what you're going to get, but if you're the wine which matches it well, then it's something you won't regret.
(tbc)