I use both Cokin "P" (for the Hasselblads) and "A" (for 35mm) filters. The "P" size filter itself measures 3.25" x 3.25". The factor limiting use would be the inside diameter of the Cokin adapter. The 60mm Bay adapter for the Hasselblads has an I.D. of 2.5" ... and I con't see where there could be enough room, using the "P" size, to go more than 2.75" - 70mm.

Other manufacturers make adapters - filter holders - for 4" x 4" filters - a good source of information would be the Calumet catalog.