Haven't tried them, but I got a copy of the optimized scrypt.cl file, which lets you build new .bin files with whatever settings you want.
On our 280x, they got us ~10Kh/s improvements per GPU. Haven't tried them on our 290s yet.
Download: (Note, not my dropbox, or files. This is just where I got it from).
https://drive.google.com/file/d/0B_EJYw4JvsnvbndpY3F0ci1BOUk/edit?usp=sharingRename the scrypt.cl files inside CGMiner to scrypt.cl.bak. Delete all *.bin files, and relaunch cgminer with your favorite settings.
Let me know how it works for you?