In the course of project site plan review, as required by this article and SEQRA, the Planning Board may, pursuant to its stated purposes, vary the zoning requirements as to open space requirements, lot area, lot frontage, side yard requirements, front and rear yard requirements, maximum allowable coverage, parking regulations, building heights, floor area ratios, unit density per acre, off-street parking and loading spaces, and all bulk regulations in connection with a specific plan of development on a specific parcel of land in any Planned Design District, and other matters related to the siting and construction of improvements listed in the Schedule of Regulations, provided that the Planning Board shall determine that such variations are in the public interest and necessary in order to foster high-quality development and redevelopment, are in compliance with the general purpose and intent of this chapter, and will ensure compatibility with uses on adjoining properties. In no case shall the variation of any requirement be greater than 60% of said requirement, unless otherwise stated in §§ 300-255 through 300-259. Such variations shall apply only to the particular site plan and proposals thereon which are under review and shall not apply to the maximum FAR.