Assuming u have a "lucky" card that can be OCed pretty well it is worth it. Figure on a 10% OC typically. The core will probaby run at 325 and the memory @ 660 or so. This will net about 500 pts in 3D Mark.
Some lucky people get cards that OC higher and some poor slobs cant OC much at all. While cooling helps, the main thing is to get a good card by luck or by Gainward's "Golden Sample" version.
Why even ask? Try it and see.