Hi,
G1 Gaming has higher base core clock, custom RGB spectrum, 1 DVI port, 3 Display ports, 1 HDMI port and 8pin power connector.
Windforce OC has lower base core clock, no RGB, 2 DVI ports, 1 Display port, 1 HDMI port and 6pin power connector, windforce is also shorter (smaller overall).
Hope it helps.
Cheers.