The way credit scores are determined for mortgage financing is by the use of a "tri-merge report" which combines your scores from all three major bureau's; Transunion, Equifax, and Experian. The middle score of the three is used for qualifying purposes.
With a score in the mid 600's you absolutely have available options, even in the jumbo market. The thing is, especially with jumbos, many lenders will have varying underwriting guidelines. Please remember that credit is only one aspect of the qualifying process. While your income looks sufficient, I would still need a better understanding of the projected sales price, property taxes, and your monthly debts (minimum payments for credit cards, any loans, etc.) in order to determine ALL of your available options.
It's best that we speak so I may gain a clearer snapshot of your scenario and advise you with the most current, accurate information. Please contact me at your earliest convenience, I may be reached directly at (201) 957-6768 or via email; whichever is easiest for you.
Paul F. Marzolla
Sr. Mortgage Consultant