Back in the day i had 3 9800gt. One was the evga super clocked at 650 900 1800. So I used afterburner to clock them all the same. Worked great. So finally I just copied the bios from the evga super clocked to the other 2 cards. Now all 3 think they are evga super clocked cards and they all run great. That was 3 years ago. 2 are in SLI in my extra computer and 1 is in my multimedia computer.
Point is those graphics cards have alot of head room so you may be able to get to 650 or 666.
Im my case all 3 video cards were refrence boards that looked identical. The boards ram and coolers were all the same.