You may wish to try out the
new version of SetiDriver and select the Force Idle Only setting
Hang on...it sounds like you are using the GUI (screensaver) version of Seti...that is very slow! And if you are wanting another screensaver (and therefore won't be looking at the graphics - which is good!) then you will be best suited with the CLI!
Clicky here and follow the instructions to set up the CLI along with SetiDriver (but use the SetiDriver linked in the post I linked above), after uninstalling the Seti@home screensaver of course
You will find that your CPU time per Work Unit will drop quite dramatically when using the CLI/SetiDriver, plus you will have the ability to cache Work Units, for when your internet connection dies, or when Seti@home's internet connection dies (which it has in the past!!), so you can keep on crunching
If you need any help setting anything up, please feel free to ask, and someone will be around to help you set up
Garry