Oh and another thing!
Best to check if you will need the Lee Push on holder for the 80XL (especially if using a 105mm Pola on the front adaptor ring) to prevent vignetting. Pretty sure that this is the case for the 90XL and 72XL which I considered at one point. The standard filter holder is then used for your other lenses. John is right about using the w/a adaptor rings if you don't have to have the push on holder. The chaps at Robert White do know their stuff and will give accurate answers.
I suggest that you avoid the square polarisers, since if used with grads, you have to have a rotating assembly clagged on the front to get the alignment right. The front 105mm ring is far neater and opens up possiblity of using Polas from Heliopan, B+W etc too. Mind you, they aren't the cheapest items to buy.