The discussion of the comparative effects of corner/ side territory vs central influence in the "LargeBoards" page made me think ... People are describing 19x19 as being optimal because approximately equal areas are enclosed by approximately equal numbers of stones on the 3rd/ 4th lines, so play is a close balance of territorial grabbing and playing for influence (in the Go sense of the word - which is clashing painfully with the English usage, which is why I'm using "effect" as a verb). Without having done the maths, it seems to me that (up to a point) this "balance" property could be preserved up to considerably larger boards by going to elongate boards.
Square Area Rectangle of similar (area) 21x21 441 19x23 (437) (obviously similar to 19x19 on one axis) 20x22 (440) (see also EvenSizedBoards) 17x26 (442) (Tibetan) 23x23 529 19x27 (513) . 19x28 (532) (getting pretty asymmetric) 21x25 (525) (comparable to 21x21)
Hmm, I think it could be worthwhile drawing up some boards like this on a sheet of hardboard or something.
BuggyMind: Shouldn't this page be called "Oblong boards"? Squares are rectangles. An oblong is a rectangle that isn't square. Of course, then there's the fact that some gobans are slightly oblong for aesthetic reasons...