hey michael,
Yes it is a wonderful thing to have a large surface.
I am afraid though that your OSB might bow since it is hanging out over the edge of your island so far. OSB is made of soft woods is known to bend after a while w/o being supported.
I made my own Big Board to lay on top of my ironing board for ironing yardages of fabric. I made the board out of 1/2" Baltic Birch plywood 20 x 60". I then covered with 2 layers of warm and natural batting, then a layer of regular muslin. Then finished off with the silver sided fabric. All this was stapled to the back of the board so it was all snug and smooth surface. This sits on top of my ironing board all the time for ironing, pressing, a work surface, etc.
I love it.
Chris