Well Even Far Cry 3 has Optimization issues still, anyone who played a decent amount of Far Cry 3 with a Higher end CPU with good Multi-threaded Performance would testify that No matter what you tweak , NCP or AMD CCC, ini files...... there is Frame jutttering and hitching. Far Cry 4 is no exception in that department. a good tool is HWifno and RTSS to see in game CPU usages in very near real time (1000ms)
After reading that a Dual Core won't even launch the game I was a bit baffled. If it is only using 1 core at 100% and the rest maybe 30% in total then why would a Pentium G3258 overclocked to 4.4GHz or higher, That can run Crysis 3 on Very High and be playable, Check out Digital Foundry's Vid/review on that one or read the review here: http://www.eurogamer.net/articles/digitalfoundry-2014-pentium-g3258-review.
This reminds me of That COD Ghosts 6GB of RAM requirement. Not entirely necessary IMPO. ..
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Unrelated Food for thought.
These AAA Ports that are using more than 3GB of VRAM may be do to teh API on consoles and how Devs will make good use of the Jaguar APU and it's Unified Memory. a game could be coded to use the 6GB of Video/System Memory on the PS4 and maybe with some tweaks Games like the Evil within would use more DDR3 System memory instead of pre-caching half our Memory on out GPUs... Again that is another topic and I hope it get's better and not be the case where every AAA game will need a 6GB frame buffer.