PHPBB Speed Issues

Hi Guys, I know this is maybe a bit specific for the general list, but thought I'd throw it out there anyway as I reckon a lot of you have had experience with PHPBB at some point or another. We've got an existing installation of the forum here, that's been active for a couple of years and is fairly busy. The site itself is on a dedicated server, but we're having some issues with the speed. Some pages are taking ≅7-8 seconds to display. I've optimised the images in the template, enabled the GZ compression, and it's only improved the speed by a mere fraction. I have noticed that the page itself doesn't display until after this delay, so I was guessing that I could maybe force the buffer to flush at key intervals to give the impression the pages are loading faster. Does anybody have any insights into this? Thanks, Ash http://www.ashleysheridan.co.uk