Can i go any further?

I have been trying to overclock my 2 gtx 560 fermis and I have had them at 900mhz no problem for about a year now. I have a aftermarket cooler on one of them and the other ones just stock. at 900 mhz on Heaven they maxed out at 70c. I want to go to 950 mhz but I tried it one time and after a while it froze on me. Am I as high as I can get?

1025 mv (voltage)
2004 mhz (memory)
900 mhz (clock)

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Heaven Benchmark v3.0 Basic

FPS:
39.1
Scores:
986
Min FPS:
6.1
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Hardware

Binary:
Windows 32bit Visual C++ 1600 Release Mar 7 2012
Operating system:
Windows 7 (build 7601, Service Pack 1) 64bit
CPU model:
Intel(R) Core(TM) i5-2500K CPU @ 3.30GHz
CPU flags:
3292MHz MMX SSE SSE2 SSE3 SSSE3 SSE41 SSE42 HTT
GPU model:
NVIDIA GeForce GTX 560 9.18.13.1070 1024Mb
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