As mentioned elsewhere, though... Extended Find is probably the primary culprit in your current performance woes... Go through your existing mapped objects, turn off the option where it is not strictly necessary, add any missing ancestor objects, lather, rinse, repeat. You'll see a MAJOR performance improvement, I'm sure.
Yes, I have turned off extended find and I have restarted all my mapped objects in a brand new project.
May be a bit drastic... you don't necessarily need to delete all your mappings and start over... I'll leave it up to you to determine which is more efficient but you can "correct" your existing mapping to add in the missing ancestors.