Well, I've got 185s for my 2x2s and I've been happy. 4x8 is 8x larger than mine, so probably at least 1000? That's quite a large table... depending on the size of your setup you may want to think about a multiple smaller ones for more flexibility.
Just do the math find the total volume of the portion of the table your going to use and the head height and buy a pump that will fill that volume in the time you want