Re: Budget Gaming ( sub 100$)
Q6600 is a fully fledged quad core, albeit an old one. If you ever watched LTT or Tech YES City on Youtube they make a lot of videos about reusing old stuff. a Q6600 is the beating heart of a lot of the 'scrapyard' builds you see on YT, because its a proper quad and they are usually dirt cheap.
6950 would be fine, for the most part. They run pretty hot and are pretty meaty though, so I'd make sure your old PC has a capable PSU (with the necessary PCI-E power cables) and at least one fan to either pull in some cooler air or get rid of the warm air.
I'd also say go for a minimum of 4GB of RAM if you want to play games, some won't even run on 2GB and most will stutter and crash.
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