Seeing as that model is already factory OC'd much like my MSI Twin Frozer HD7950. If it has the 6-Pin and 8-Pin power connector it may be using the HD7970 PCB.
The Sapphire Dual X HD7950 is at 925Mhz at 50Mhz more at 975 Mhz that is basically stock clocks for an HD7970
Refer to this for the type of performance you'd expect - http://hexus.net/tech/reviews/graphics/34761-amd-hd-7950-vs-hd-7970-clocks/
1100Mhz should be easily done which is even better then link above without even adjusting stock voltages. Of course like all things your miliage will vary you may need run some sort of benchmarking utility to confirm stability without any sort of artifacting.
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