The answer usually relates to whether the Allopathic Board in your specialty will accept your prior training in an osteopathic program. There is little sense in switching if you will not be board eligible, or they require you to repeat several years. Typically, however, Allopathic Boards require completion of a certain number of years (depending on the length of training) in an ACGME approved residency.
However, you would be best advised to contact the board in your specialty and see what the party line is; can you get credit for time in an osteopathic residency, can you be board certified without repeating those years? If they give you a positive answer, get it in writing because allopathic PDs will want to see that. They are not interested in training people who cannot be board certified and you can find yourself in the unenviable position of being unable to be BE/BC by any board (osteo or allo).