Turning off titles would make no impact on performance... if you wish to reduce how quickly people post in a really effective manner, try using a flood check time of, say, five minutes or so. Though that may get people to complain a bit... <img src="https://www.ubbcentral.com/boards/images/graemlins/wink.gif" alt="" />
I notice you have a number of hacks installed. First things first - get rid of the hacks. The statistics hack in particular is a known server killer.
Next, upgrade to 6.6.2, or 6.7 when it's released (very shortly). There are a couple enhancements in those versions that may help things out.
Take a peek in your control panel - what's the cache hit percentage listed on the control panel intro page?