Please note first that nVidia graphic cards aren't ordered by performance with the version numbers (they go down and up per series).
260GTX...
216 Processing cores
Graphics Clock (MHz): 576 MHz
Processor Clock (MHz): 1242 MHz
Texture Fill Rate (billion/sec): 36.9
Supports DirectX 10
285GTX...
Two GTX260 glued together
Specs similar to that of the 275GTX
460GTX has...
336 Processing cores
Graphics Clock (MHz): 675 MHz
Processor Clock (MHz): 1350 MHz
Texture Fill Rate (billion/sec): 37.8
Supports DirectX 11
With the 460GTX there is a difference between the 768MB and 1GB version of about 5-10fps @ high resolutions. At both 1680 and 1920 resolution, the 1GB GTX 460 is roughly 10% faster than the 768MB card.
460GTX Memory (1GB GDDR5 vs 768MB GDDR5)
Memory Clock: 1800 (same)
Memory Interface Width: 256-bit vs 192-bit
Memory Bandwidth (GB/sec): 115.2 vs 86.4
260GTX Memory
Memory Clock (MHz): 999
Standard Memory Config: 896 MB
Memory Interface Width: 448-bit
Memory Bandwidth (GB/sec): 111.9
Bench mark will depend on your other computers specs and game,
but as a basic idea (using the same specs except card):
Crysis: Warhead - 1680x1050 - Gamer Quality
Nvidia 460GTX (1GB) - 41.1fps
Nvidia 260GTX (896MB) - 27.4fps
Crysis: Warhead - 1920x1200 - Gamer Quality
Nvidia 460GTX (1GB) - 33.8fps
Nvidia 260GTX (896MB) - 22.7fps
Crysis: Warhead - 2560x1600 - Gamer Quality
Nvidia 460GTX (1GB) - 19.2fps
Nvidia 260GTX (896MB) - can't handle
At high resolution, the fps difference is around 10fps increase with the 460GTX.
Lower resolutions improve up to 20fps with most games.
