Though the marriage can be performed under foreign marriages act, 1969, the provisions of special marriages act shall apply to this type of marriage, i.e., for the marriage between an Indian and a foreigner.
1) Do I need to seek prior permission from the Bank before marrying a foreign national ?
As you are bound by the staff regulations of teh State Bank of India, you may have to abide by the rules of the bank in this regard. The rule in this regard is: An officer employee who has married or marries a person other than of Indian Nationality shall forthwith intimate the fact to the Bank.
2) Will my wife be entitled to all the benefits that the spouse of an Officer in the said Bank gets?
After being permitted to marry the foreign national, she shall be your legally wedded wife and she is entitled to all the applicable benefits, which is described under the definition for family:
In the case of male officer employee, his wife whether residing with him or not, but does not include a legally separated wife and in the case of woman officer employee, her husband whether residing with her or not, but does not include a legally separated husband.