Far Cry 3 didn't look that good, my old GTS 450 could easily handle it on Ultra presets. Secondly Far Cry 3 is based on the Dunia 2 engine, which is a revision of the original Dunia which itself was based on the original CryEngine, which Ubisoft acquired when it bought the Far Cry IP those years back after the first Far Cry. The original Dunia engine probably retained around 14-18% of the original CryEngine's code and the Dunia 2.0 engine would have probably retained around 4-6% of the original CryEngine's code.
The first Crysis was then powered by CryEngine 2 and Crysis 2 powered by CryEngine 3, although utilizing only say 45% of the engine's capabilities at the time, the reason for this was that many complained that their system couldn't run the original Crysis and the limitations of consoles, but as Crytek worked with the consoles the more their knowledge of console software and programming grew and allowed them to make better use out of the consoles, so they set out to rip CryEngine 3 to pieces to get it to work well on consoles and the end product is CryEngine 3.4 (the console version), which Crytek's CEO says maxes the consoles out, to their limit with not even 1% of energy left available. Crysis 3 will be powered by CryEngine 3.4, an engine which was developed to max out PC's but was then ported to consoles.