That's the issue I mentioned with Invision. It has a lot of tables, so it uses extra CPU (not much, but noticeable if you look at the task manager). I'm curious about the 5MB table. What's it for? Hash tables are good for data that is used frequently (usually, that means that the table is fairly small). If you have data stored that isn't used often, then saving it to a file is probably better.
You could easily find out if that's the problem by freeing the table and checking your CPU usage.