I'm a little late on the topic, but as I used to say in the Air Force...... The best thing about being an E-5, is that you have to be one to be promoted to E-6.
That said, if you don't take the promotion, not only are you not likely to be offered anything better than what you have now, they may not want to keep you because you don't {look to them like you} have enough drive.
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