#1 way to increase things is RAM, RAM, RAM

if you think InooDB helped you, then more power to you... i won't try to disuade you

$99 is hard to beat....
but, like i said, an 8GIG RAM server dedi is looking at
$149 $129...
but to get 3 HDDs, you aren't gonna beat $99...
at some point, though, unless you prune old posts, the forum will grind to a halt and be unusable....
and you will find that it won't be a SLOW thing.. it'll suddenly go over a cliff and just be unresponsive..... you are getting close to that limit, if saving posts cause a huge delay already
