His CPU is slightly overclocked, and his frame rates are practically unplayable with his current settings. To get 45+ you'd need to play on the lowest of settings and at that, what's the point?
Also, I call total ******** on his videos. He's not running the hardware he claims because I made videos on Watch Dogs running different settings, different CPU core tests, and running a highly overclocked GTX 680 got between 50-60fps at 1080p. I also ran "theworse" mod to up my framerates using that other guys texture modified and it only granted me about 5fps. My average was about 50 with high textures, ultra settings, and DoF/Blur off. My VRAM was over 3GB and this guy is only at 1GB. My system RAM usage was also about 3.5GB and his isn't even around 3GB.
Don't believe everything you read or see on the internet. You got your 15% CPU figure off of CPU-World I'm betting and it's wrong. The Q9*** series was nothing more than a die shrink and clock increases. No architectural advantages to increase speed that far. Considering the fact that I've actually owned a Q8200 and Q9550 I might know a thing or two about them.
Bottom line here, I'm not telling you it won't work. Just don't expect miracles like that Youtuber. If he had a more powerful GPU in his claims it would be believable, but he lists a 650 which is pretty weak. My old overclocked 580 got only slightly higher frame rates than what he's claiming to get and it's more powerful than a 660, which is significantly more powerful than a 650.