720Mhz OC'd to 763Mhz is only like a 5-6% overclock. So in theory, you'd see 5-6% better performance. Although, it doesn't always equate equally like that.
If you'd rather save the $20, I'd say go for it!
Honestly you could overclock the standard video card to 763Mhz by yourself more than likely. Though you probably don't need to.