Time to move out of GUIMiner. I recently graduated from GUIMiner to the other Windows tools where you can set more flags, or config files. With a little reading and skimming through the main threads for respective miners, it's pretty easy to get a good sense of how to get it working. There's always the Google search on things like "how to setup cgminer on win7", etc.
I went from GUIMiner to Phoenix 2.0, to CGMiner. I really liked CGMiner and wanted to make work because of the integrated ability to OC and control fan, but was having pool connection issues and was turning in a whole bunch of stale and invalid shares (0.8-0.9% over 24 hours). Now I'm back on Phoenix 2.0 doing all my overclocking with MSI Afterburner (OC limits unlocked via .cfg) and things are good. I'm squeezing more mhash out of my cards compared to GUIMiner, and my stale/invalid is starting to recover.
Thanks for your informative post! I do already use MSI Afterburner, so I might follow your steps and try out Phoenix 2.0. Seeing as I can do 1300/330 with no tweaking, it should only get better.