Your problem is keeping a spare task for your 9800's - Don’t.
Tasks that complete within 2 days are very useful to the project, but after that they are of little or no use. In fact they are a bit of a problem. So keep your cache for your 9800 systems at 0.01 days.

Your "spare" task is not even running before it becomes of little or no use to the project; after 2 days the task is resent to a fast card and will probably be returned within 8h. As it will return before your task, your efforts would be redundant.

Even for the GTX460 I would suggest a cache of about 0.2 days.

Unfortunately you cannot configure Boinc to keep a small cache of GPU tasks and a large cache of CPU tasks. You can only make a universal selection to keep a low cache. I also don't like this situation but I can do nothing about it. Feel free to make a proposal to Berkeley.

In Boinc manager, Advanced Preferences, network usage, make sure that the connection options are both unchecked (Confirm before connection to the internet, and disconnect when done).
Under the Activity Tab, select Network activity always available.