forums by their nature are typically slower then other types of websites and well this is a an older, somewhat heavily modified vB forum backend.
Most of the slowdowns is due to other users using the same db tables you need (they get locked for each query) and distance (for quick reply and other ajax features, your computer's power and speed play a large role) from the server, as well as time of day.
remember, if you're posting or opening a non-popular thread, the site has to locate, load and serve the post data (some popular ones are cached as they're accessed more often) all this takes time, yes sometimes as long as 10 seconds. the database is ~9.25GB thats a lot of data to look thru.
Now about pageviews, tPC gets about 90K pv a day on average currently. Yesterday we had exactly 252,723 page views.
p.s. this was a quick reply and took less then 2 seconds to process and load the page.