As said above, the GPU will be the more important component for Far Cry 3. As for which CPU is better, the i5 is overclockable and will fare better in games that can use more than 2 cores eg. Battlefield 3 Multiplayer. The i3 2100 can't be overclocked, but will do better in games that only use 1 or 2 cores if you have sufficient graphics hardware to cause your games to become CPU bound. For the vast majority of games though, you will be GPU bound and it won't make a huge difference which of those two CPUs you have. Either chip will keep up with today's graphics cards.