How bad of an impact would removing the search limits on Enhanced Search cause? Currently, we have it set to 200 results, which on a busy board, could be only a few hours worth of posts, especially when using the "New Posts" link. Some of our users are complaining that they're missing content due to new posts/threads not being displayed. It's not uncommon for the site to receive 8-10 thousand new posts in a day.
@Biker just increase it to 500 and see how it impacts (or not) and then increase it at intervals until you find the point at which it causes a slow down. I imagine if it's a large and busy site it'll already have the hardware and set-up to accommodate a much higher search results setting.
Of course there's a practical limit too; just how many pages of results is someone generally going to bother searching through?