Far Cry needs optimization. I can run it, barely, at medium settings (25-40fps) with my 1.5ghz Gf3 Ti500 and 512 ram machine. Yet UT2004 MP runs smoooooth maxxed out. And, it has better graphics, to boot.
Are they the same game engine? Some games are just like that, ya know. Take UT2003, Tony Hawk, and Simpsons: Hit & Run for example, they're all the same engine, which is why the game is almost fluid.