GT520 is pretty identical to GT610. I think they are pretty fine, though not the greatest stuff. But on such low end cards you have to compare the memory speeds (varies per vendor and specific model) and get the model with the faster memory (i.e. if one has 535MHz memory and another one 667MHz, the latter is much faster)
GT440 is much faster, by far the best one on the list. Actually strictly the same gen than the 520 and 610. But uses more power which is maybe significant if the gas guzzling Pentium 4 is on a 250W PSU in a very cramped case.. But that's not too much of a biggie. On this card, no silly game with memory or 64bit bus (GT430 with 64bit bus can exist I think, then it's a rip off)
Old cards like 6800GT, 7600GT were up to the task for the games and res you cite (cranked up all the way with AF and AA), I think a GT610 performs about the same. With GT440 you can probably play fine with 16xS AA for instance, or 8x MSAA.. With Far Cry, set some 4x or 8x MSAA, enable transparency AA in supersampling mode (this is done in the driver or something like nvidia inspector. It's best in a game profile).
Then Far Cry 1 looks totally gorgeous lol. Default setting (for all games except those that get a profile) can be 16x AF, and "8xSS" (mode made from 2x multisampling + 4x supersampling), "high quality", perhaps vsync + triple buffering.
Good time to upgrade from XP to Windows 7 if it hasn't be done (malware fest coming soon). New thermal paste maybe.
