Because they have the same part number (but different revisions as indicated by the letters), you know that there have been no major design changes and they will work with the same software. The revision changes have been incidental, like a change in a part or something.
Alisha is correct that the changes should generally not be noticeable, and the same drivers will work with both. The most significant change is that Rev G works only with 5V PCI slots, while Rev K works with either 3.3V or 5V slots.
