Assuming you've tried the steps in the posts at the start of
this thread and they haven't gotten things as speedy as you'd like, the next thing I'd look at is the project tree.
Particularly big or complex ones increase the amount of work OmniFocus needs to do to keep everything running. There are more due dates and styles cascading around, for example.
One thing I've seen from time to time are customers that have a couple hundred (or more) someday/maybe projects in their database. I can understand deriving some comfort from having those projects around, but the cost of that approach is a slower app when you're actually getting work done.
If that sounds like it might be related to what you're seeing.n general, I recommend moving those into a
secondary OmniFocus database and keeping main database for projects that are actively being worked on.
During reviews, just double-click the secondary database - you can then drag projects back and forth as needed to move them onto or off of the active-work list.
Hope that helps, but if it doesn't, describe your setup in more detail and we'll be happy to assist.