How about a block that rather than updating the posts on each board refresh, it would only list the "X" recent posts in the past, say, five minutes? Or ten minutes? I remember that supersmashbros' ibMarket mod did something similar when it came to giving money for posts. It's not perfect for a large board but perhaps it's an alternate solution? I'm not sure if the exact details but it would at least be fine for my board, I think.