Went in 2011.
Assuming this year is anything like 2011, you will not need a 4 day ticket.
Me and my friends saw everything easily in about 4 or 5 hours. If you did want to try out every game etc. then 2 days would be sufficient.
Something to bare in mind though if you really want to go for 4 days is that there is scope to profit from going. When I went I got multiple CSGO beta access cards which I managed to sell for about 40 pounds each.