when you play at 720p the burden falls mostly on your CPU, at 1080p the burden is transferred over to your GPU. with your specs you should have no issue with doom2. skyrim will play OK at high settings (not max) as should borderlands 2. I don't know much about chivalry.
techspot has hardware reviews of skyrim and borderlands 2 but expect the Q6600 to give you athlon II x4 performance
the good news is the Q6600 OC very well