this is just as a side note, but generally what you want to do is keep size on the Session and ViewState small. I generally just store IDs and small amounts of packets in Session and ViewState.
for instance if you want to pass large chunks of data from one page to another, you can store an ID in the querystring and use that ID to either get data from a database or a file.
PS: but like I said, this might be totally unrelated to your query :)