Unless you can somehow convince BMWNA to give you the 3.9%, refinancing with a third-party lender will not lower your rate.
Risk-free treasury bonds are paying around 5% right now. No matter what your credit score is, you are riskier than lending to the US government (at least in theory). If people are lending to the US government for 5%+, depending on term of the loan, they're not going to lend to a riskier borrower for less interest. The only reason BMW NA can offer those rates is because they are incentivizing you to buy the car. The reason I bought the car was because I found the 4.9% attractive (I bought it less than 2 months ago so I share your pain).
Not sure about how it would affect your credit score.
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2008 335i | Space Gray | Blk & Gray Poplar | 6 MT, M3 Lip, Painted Reflectors, Huper Optik 30 (35%), V1 Hardwire, Pussy Magnet
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