Q: slow performance in iPhoto

As a Test:

Hold down the option (or alt) key and launch iPhoto. From the resulting menu select 'Create Library'

Import a few pics into this new, blank library. Is the Problem repeated there?

It was a test...

Back to the original library:

Option 1

Back Up and try rebuild the library: hold down the command and option (or alt) keys while launching iPhoto. Use the resulting dialogue to rebuild. Choose to Repair Database. If that doesn't help, then try again, this time using Rebuild Database.

If that fails:

Option 2

Download iPhoto Library Manager and use its rebuild function. (In Library Manager it's the FIle -> Rebuild command)

This will create an entirely new library. It will then copy (or try to) your photos and all the associated metadata and versions to this new Library, and arrange it as close as it can to what you had in the damaged Library. It does this based on information it finds in the iPhoto sharing mechanism - but that means that things not shared won't be there, so no slideshows, books or calendars, for instance - but it should get all your events, albums and keywords, faces and places back.

Because this process creates an entirely new library and leaves your old one untouched, it is non-destructive, and if you're not happy with the results you can simply return to your old one. 

Regards

TD 

How much free space do you have on your hard drive?

OT

That kills a brilliant hypothesis.

Maybe the new library ends up worse than the old one.  That's something you'll have to examine and decide.

This the one you have rebuilt with Library Manager? If it works correctly and has all your photos trashing the damaged one seems a likely course of action.