Just go with the I3. It should do what you want. Don't expect everything to run smooth but it will get the job done with most games. 4gb is fine.
Intel I5 2500k 4.6Ghz@1.34v w/ Noctua NH-D14
Asus P8P67 Pro
OCZ Agility 2 60GB SSD
G. Skill RipJaw X 8GB 1600
EVGA GeForce GTX 560 Ti Superclocked
Creative X-Fi XtremeGamer Fatal1ty Pro
Thermaltake ToughPower 750W
Rocketfish Aluminum Full Tower Case
Asus P8P67 Pro
OCZ Agility 2 60GB SSD
G. Skill RipJaw X 8GB 1600
EVGA GeForce GTX 560 Ti Superclocked
Creative X-Fi XtremeGamer Fatal1ty Pro
Thermaltake ToughPower 750W
Rocketfish Aluminum Full Tower Case