Ok first, make sure your flashing the LN2 bios nly. EVGA will warrent any warrenty returns due to a fried board from overclocking as long as the first bios is stock. You can flash it back if you have saved the bios and have already flashed over it.
Now to flash my GTX 780 Classified, I used Ez3Flash from here. http://www.overclock.net/t/1438886/official-nvidia-gtx-780-ti-owners-club
Make sure you dont have a PLX chip on your motherboard. If you flash over your PLX chip you kill your motherboard.
Now you dont actually need to flash the bio to overvolt past the current max. All you need is this. http://kingpincooling.com/forum/showthread.php?t=2514
This will take an GTX 780 Classified to 1.35v max or ti 1.5v. Only mess with the first setting as the second one is memory and unless you know what memory module you have, you could easily fry your memory. The third is how much power you are drawing from the PCIe bus. This can also fry your motherboard if you draw too much.
Now there is a major difference in design between the 780 classy and the 780 ti classy. the 780 was designed with a better VRM. It was designed beofre nvidia screwed everyone over with TPU max across the board. Its still better than stock but keep that in mind.
Bios wise, skynet is fine http://www.overclock.net/t/1438886/official-nvidia-gtx-780-ti-owners-club. Bios isnt important as you might think. As long as its the new revision which I believe it is.
Now my results will show a higher clock because I have a 780, not a 780 ti but this is what I get.
ambient temperature 16C, Voltage 1.2, clock speed of 1253, fan speed 60% temp 79C
ambient temperature 16C, Voltage 1.25v, Clock speed 1303, fan speed 73% temp 84C
ambient temperature -1C (I opened the window on a cold winters night and waited till morning for this clock), Voltage 1.35v (Not recommended) Fan speed 100%, Clock speed 1520.Temp 93C
Now heres the thing with overclocking these cards, Only over volt further when you see artifacts. If your not seeing artifacts in your benchmarks then you can push harder. The higher you go voltage wise, the more risk you have. The only way I can get passed 1.35 is if I physically replace the resister on the card. obviously void of warrenty. Not that I can push any harder without water.
If you push voltage up too high without raising the clock speed, you risk doing damage to your card. You need to bring them both up gradually. taking small steps at a time. If the card is getting hotter the more you push the voltage to the point its in mid to high 80's and your getting very little overclock from the voltage, Stop and back off. your card wont do much more.
I run with my card at 1.21v 1253 clock with an added 700 on the memory but some cards have different memory and basicly if you dont have samsung memory, You wont be able to overclock your memory.
These cards can get insane overclocks, just dont expect gods gift of overclocks and even if you get a very nice overclock, dont expect to be able to run it day by day without consequence. i run with an extra 0.01v on the core to make sure I dont have stability issues as some games work the cards harder.
Also remember that the fan draws power too and as it increases, the TDP usage also increases. reason why I can get passed 1.21v on stock bios is because the fan ramps up enough to hit the 115% TDP max.