Admittedly PHPBB is currently behind the competition in terms of features, but that's because their 2.2 release was delayed to a 2005 release.
Sometimes it takes ages to post a topic but that doesn't happen very often. When they modded the forum to add the spam section as a subsection of General (not possible in PHPBB 2.0.x by default but a feature built into 2.2), I did notice a lot of lag in that particular section but this appears to have been fixed now. The General section is still slightly slower than the other sections but not significantly.