Many visemakers cataloged 8, 9, and 10 vises. But, I dont think they sold too many of those. A 200+ pound tool can be unhandy.
A friends grandfather had a 8 Prentiss. When the old guy died, it didnt sell at the auction. I think it ended up in a pile of scrap. I could have had it for nothing.
But, it was beat pretty hard, and was more than I weighed, or, even more then I weigh now.

Best,
Ted