All questions about BIOSs/benchmark results/overclocking technique, etc., for the MSI GTX 770 Lightning posted here. I will try to help you out as much as I can.
This card's GPU 2.0 boost uses 13 MHz steps (1320 MHz, 1333 MHz, 1346 MHz, etc.). You have to check MSI Afterburner, to find out what GPU 2.0 boost you're running at when benchmarking. When you reach a 13 MHz step which is unstable, just dial back the core clock 1 MHz (back down to the last 13 MHz step), and you should be at your highest stable overclock.
My own overclocking results:
GPU Clock: 1254 MHz
GPU Boost: 1306 MHz
GPU 2.0 Boost: 1346 MHz
Memory Clock: 7800 MHz
Afterburner settings:
Core Voltage: +100 mV
Memory Voltage: +100 mV
Aux Voltage: +0
Power Limit: 125% (increased with Kepler BIOS Tweaker)
Temp Limit: 95°C (prioritised)
Core Clock: +104 MHz
Memory Clock: +400 MHz (lowered default to 3500 MHz in Kepler BIOS Tweaker)
Fan Curve: 10%/0°C, 100%/70°C
Unigine Heaven 4.0 Results (highest settings possible, no 3D, single monitor, 1920 x 1080):
Final FPS: 44.5 FPS
Highest Temp: 78°C (after 3 loops)
This card's GPU 2.0 boost uses 13 MHz steps (1320 MHz, 1333 MHz, 1346 MHz, etc.). You have to check MSI Afterburner, to find out what GPU 2.0 boost you're running at when benchmarking. When you reach a 13 MHz step which is unstable, just dial back the core clock 1 MHz (back down to the last 13 MHz step), and you should be at your highest stable overclock.

My own overclocking results:
GPU Clock: 1254 MHz
GPU Boost: 1306 MHz
GPU 2.0 Boost: 1346 MHz
Memory Clock: 7800 MHz
Afterburner settings:
Core Voltage: +100 mV
Memory Voltage: +100 mV
Aux Voltage: +0
Power Limit: 125% (increased with Kepler BIOS Tweaker)
Temp Limit: 95°C (prioritised)
Core Clock: +104 MHz
Memory Clock: +400 MHz (lowered default to 3500 MHz in Kepler BIOS Tweaker)
Fan Curve: 10%/0°C, 100%/70°C
Unigine Heaven 4.0 Results (highest settings possible, no 3D, single monitor, 1920 x 1080):
Final FPS: 44.5 FPS
Highest Temp: 78°C (after 3 loops)