You want your closing statement to be the Mariano Rivera of letters of intent: a clean win, effective, and unambiguous. Don't overthink it! Basic, professional closings are the way to go.
Go with one of the classics, because they're used for a reason. If you sound too stiff and formal, it comes off like a holiday card. If you reiterate your call to action, it can carry a whiff of desperation. Just get out gracefully and quickly once you've said your piece.