This seems VERY VERY high for a 560Ti overclock. Most cards struggle to get 1000MHz core. How long are you running a test for? What are you using to test?
Running a benchmark for a few mins WILL NOT test overclock stability. You need to run a proper GPU burn-in/stability test for at least 30mins to test it properly. Most people will probably suggest even longer.
core clock: 1000
is usually very close to the max. I don't understand how your getting temps of 71 with stock voltage. Something doesn't seem right...
I suggest download OCCT (Linky!) and using the GPU test with error checking enabled. That will tell you whether or not your overclock is actually stable. Run the standard hour-long test at your full screen resolution with error checking and logging enabled. It will create a nice pic that logs your GPU temp and frames per second over the test period.
i wouldn't push it any further, the numbers you're giving are allready a lot. I have an Gigabyte 560 TI SOC ( factory overclocked to 950 mhz, 1950 memory clock and it's running with a voltage between 1.04 and 1.1 V ) With lower voltages it crashes. First gigabyte had SOC cards up to 1000 mhz but there are reports of a lot of problems with the GPU. ( like "exploding"and all ) They didn't lower the clock speed in the newer cards for nothing i think . . . Anyway, keep an good eye on the temperature, mine doesn't come above 66C but the two fans are working like crazy to keep it that cool.