If an income, estate, or gift tax charitable contribution is allowable for any part of the property transferred, the taxpayer may elect to use such Federal midterm rate for either of the 2 months preceding the month in which the valuation date falls for purposes of paragraph (2). In the case of transfers of more than 1 interest in the same property with respect to which the taxpayer may use the same rate under paragraph (2), the taxpayer shall use the same rate with respect to each such interest.