Good job with your English.
The difference between the two cards is this: the 768MB version has less texture and ROPS processing ability. So it's inherently slightly slower.
The BIGGEST difference, is memory and abilities at higher resolution.
If you're playing games at 1680x1050 and higher, the 1GB GTX 460 is probably the better bet. At a lower resolution, the 768MB version is perfectly fine.
However, unless you're playing at 1920x1080 or higher, there's really no point in using two of them to begin with.