In regards to voltage, 1.25 is good if you have good temps there.
For a nice 24/7 OC, my advice is find a voltage range where you can run IBT/Prime and stay at 70-72ish MAX.
You will never reach these temps in any real world situation, and thats probably going to be around 60-65c at the most for the heaviest real world load. Gaming 50-55c at the most.
Sure, you can go higher. And for heavy OCing thats one thing. But to find a good 24/7 OC this is the envelop I like to stay in.
What I would do is manually set the voltage to 1.25 (or whatever your particular setups comfy spot is).
Use Load Line Calibration, Vdroop OFF or whatever its called on your MOBO.
Leave all of Intells power saving utilities on. EIST etc.
Then start testing. For these quick tests I would use IBt 10 pass Normal. The idea is pass 10 tests (takes just a few minutes) untill you get errors at that voltage. NOT BSODS just errors.
Then, bring the multiplier down a notch and run Prime Overnight. If its stable at 10-12hrs, your good to go.
All CPUs are going to be different. For example my 2700K can run up 4.5ghz with ease. Really doesnt need anything extra to do it either. But at 4.6 it starts wanting more juice. 4.7 is a big jump and from there it just starts getting more and more. I can run it at higher clocks but but power it wants and heat it starts generating just isn't ideal for 24/7 IMHO.
Of course, that also depends on personal preference. Some like to OC for every last mhz of performance without regard for power consumption, heat, or voltage. And thats fine too. Just IMHO, those types of OCs are best for benchmarking not 24/7 use.
Time and patience. You'll find that spot where everything work beautifully together.