I was doing some messing around with the latest gui-miner client and found that the cuda miner is way more efficient at mining than the older gui-miner. With using the 5-21-11 version, I was averaging around 60Mhashes/s on an MSI gtx560Ti. I upgraded to the new gui-miner dated 6-9-11 and found I had some options for the cuda miner (maybe the old one had it and I missed it lol). I started an instance and kept my old flags of -f20 and -w128 and found out my Mhashes went to 85Mhashes/s. It also removed the desktop lag I was having.
You just go to the location in the screenshot(File->New Miner->New CUDA Miner) to get a new instance of the miner and enter your login information like you normally would.
I changed my flag of -f20 to -f1 in the screenshot and noticed really no difference in Mhashes, but my GUI lag came back. I set it back to -f20.