Two questions about overclocking

[ZenMonkey]

I have an i5-4690k. I've had it in three different systems, and each system has a different overclock threshold.

 

With my old Gigabyte GA-Z97-HD3 (Rev 2) motherboard, I was able to get 4.4GHz stable at 1.28v

With an ECS Z97I-Drone ver 1.0a motherboard, i was able to get 4.2GHz at default voltage, but any attempt to push higher was unstable

Now, I'm using an ASRock Fatal1ty Gaming Z97X Killer motherboard and I'm only able to get 4.3GHz at 1.275v. I've tried to get 4.4GHz as high as 1.31v but it's not stable.

 

So my two questions are:

1) How high can I safely push the voltage on my 4690k assuming I keep thermals in check?

2) Why does stable overclock vary so much from one board to the next?

[Coaxialgamer]

I wouldn't go above 1.4V on haswell imo . What you'll get out of that voltage depends on your chip .

As for your second question , it's possible the power delivery is what is causing the difference in overclocks . Other things , such as LLC and p-state settings could be causing those issues if you don't pay attention

[InsanityWolf]

Unless you get the top of the line chip,other lower end chips are basically a bigger chip that maybe had a malfunction to their cores or speeds,and thats why they are sold for less compared to the most high-end of a series.So for one i5 that is at its heart an i7 the core clock was ok and only hyper threading and some extras were disabled,while the other i7 had problems with its core clocks but because it gets downgraded to an i5 it must not have hyper threading and other stuff.

[Coaxialgamer]

13 minutes ago, InsanityWolf said:

Unless you get the top of the line chip,other lower end chips are basically a bigger chip that maybe had a malfunction to their cores or speeds,and thats why they are sold for less compared to the most high-end of a series.So for one i5 that is at its heart an i7 the core clock was ok and only hyper threading and some extras were disabled,while the other i7 had problems with its core clocks but because it gets downgraded to an i5 it must not have hyper threading and other stuff.

Fun fact on binning . I'm willing to be the majority of i5's have functionning hyper threading hardware , simply due to the small amount of hardware required . An often overlooked difference between the i5's and i7's is cache amounts (6 vs 8 MB l3 ) . Cache takes up a considerably larger amount of die area , and it's likely i5's just have defective cache blocks.