I'm on r6897 and I'm seeing the difference, it's not really that big for 4x, try 9x and find a good contrast. Remember, although SSAA is costly, it delivers the same quality for the edges as regular edge antialiasing, which you would usually set to 16x for really high quality
Specs: intel i5 3570k @ 3.4GHz;
16Gb RAM; Raedon HD 7900;
Win8 64-Bit
16Gb RAM; Raedon HD 7900;
Win8 64-Bit