Trouble OC'ing my GTX 560 Ti

So I just got My new Gtx 560 ti and when i overclock (even very slight increase) I'm getting worse FPS. This has never happened to me before any help would be great. Also when I Overclock i run FurMark and the card seems stable i dont get any of the tell tail signs of an unstable OC.

Specs:
Operating System: Windows 7 Home Premium, 64-bit (Service Pack 1)
DirectX version: 11.0
GPU processor: GeForce GTX 560 Ti
Driver version: 275.33
DirectX support: 11
CUDA Cores: 384
Core clock: 850 MHz
Shader clock: 1701 MHz
Memory clock: 2052 MHz (4104 MHz data rate)
Memory interface: 256-bit
Total available graphics memory: 4095 MB
Dedicated video memory: 1024 MB GDDR5
System video memory: 0 MB
Shared system memory: 3071 MB
Video BIOS version: 70.24.11.00.62
IRQ: 16
Bus: PCI Express x16 Gen2

Computer specs:
Windows 7 64 bit Sp1
i5- 750 OC to 3.2ghz
8 GB DDR3-1600 G.skill Rip Jaw memory
Corsair AX850W 70A 80+Gold Power Supply
WD Caviar Black 1Tb HD

Id recommend using MSI afterburner to overclock. Personally my GTX 560Ti runs a very nice stable overclock at: 1075 Core Voltage, 950MHz Core clock, 1900 MHz Shader, 2100 MHz Memory Clock.

When your testing overclock settings, i recommend using Unigine Benchmark test instead of FurMark aswell. Its a really nice benchmark run and takes about 4mins from start to finish. Settings are easy to alter, and it gives you a great break down at the end.

Nice set up by the way

Mine is @ 1000 core @ 1.112 volt.

The problem is not the overclocking, but the SLI. Download the newest SLI profile patch from Nvidia's website here, and try the overclocking again. Also make sure you have the newest graphics card drivers (newest ones are 275.33 I think) from the same website. Also remember that few games are optimized to handle twin GPU's well, so you often get better performance from a single powerful GPU than with two less powerful GPU's. It's just how it works.

Oh yes, and avoid using FurMark. It overstresses the GPU and shortens its life dramatically without reason. 3DMark, Kombustor or similar things work just as well, but saves the GPU from higher temps and stresses.

Ah it seems Tom's Hardware's url tags work a bit different. I apologize. The patch is a 2009 version, I know, but it sometimes work wonders in SLI setups. Also remember to check the temps of the top card in the SLI setup, as it always suffers added heat from the bottom card as well, and when coupled with overclocking can easily lead to a super-hot GPU and crappy performance.

I have the Gigabyte GTX 560Ti OC (came pre-overclocked at 900MHz) however that shouldn't make too much difference, as long as the GPU has adequate cooling 950+ MHz shouldn't be too hard.

When you say "make sure of your voltages" what do you mean? I have the same card and want to Overclock it to Adrians specs but I don't know if I need to change the voltages from stock 1062 --> 1075 like adrian.