I don’t think anyone can give you a very helpful answer without seeing your position on your current bike.
That being said, I’m having trouble wrapping my head around someone 6’4 riding a 57cm frame.
I”m 6’1”, and fit fine on a TCR XL setup with 4-5” of drop seat to bars and plenty of rom for more.
Unless you have gorilla arms, or are running an insane amount of drop from seat to bars, going down a frame size seems like it would be a difficult fit.
Again hard to sat without pics though
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