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Intel Core i7-875k and i5-655k processor review

Initially I didn’t have high hopes when overclocking with the modest Intel DP55WG motherboard and I already had a standby Asus board waiting in the wings for this page. For those of you who have read our preview posted earlier then you will know that this board really did rock our world.

The only issue with the board was increasing the BLCK – it did not want to go above 133 for us regardless of voltages or any other settings. We actually hosed the Windows 7 64bit OS a few times which was painful.

Using simple multiplers however we were able to get the Core i7-875K to a whopping 4.8ghz.

To achieve this, we used the Noctua NH D14 cooler – or as I lovingly refer to it – ‘The Austrian Sandwich’. We would also like to thank Crucial for sending us over 6GB of their awesome Ballistix Tracer for this review.

This cooler is without a doubt my favourite on the market right now and I have achieved results very similar to good water cooling. It is a brute for sure but the results are unmatched on air and it has a place in my heart now for every serious build I create.

The Intel bioses are a little ‘strange’ when compared to a standardised bios from say, Asus. But if you know what settings to change, the results can actually be very impressive. As I mentioned on the last page, the WG motherboard has only a very simple 4 channel CPU power circuitry and Intel themselves recommend to use the higher end board for the 875K. We actually achieved higher overclocks with this Intel board than several others we compared with later.

Forcing the multiplers to 36 we had to increase voltage override to 1.2375V – which translated to around 1.42 when we increased the current limit override and power limit override as well as adjusting the Vreg Droop Control to performance mode. Without the Vdroop at this setting we were limited to just over 4ghz. Idle state was set to high performance. These settings combined with a few others means that the CPU will always stay locked at the 4.8ghz clocks, regardless of how many cores are loaded.

Ultimate air setup - Raven 02 & Austrian Sandwich - with an extra fan on top, just for good measure

Using the Noctua cooler we recorded idle temperatures of around 35c and load around 87c (compared to 28c idle and 48c load at reference speeds/voltages). Reducing clock speeds to 4.6ghz and correspondingly lowering voltage slightly, we were able to reduce load temperatures by 10c … which is probably a more realistic long term setting, if you are happy losing 200mhz performance. We obviously ignored our instincts and left the system benchmarking overnight at 4.8ghz, partially expecting it to have BSOD’d when we returned …. but we were happy to see the looped tests still running.

Scaling is impressive and clearly the Austrian Sandwich is coping with voltages right on the limit as no throttling is taking place at these insane clock speeds.

Overclocking the Core i5-655K also gave staggering results and although we ran into the same BCLK issues over 133 we managed to hit a multipler of 133×36! This gave us an end result of around 4.8ghz.

We did get the system to boot at 5ghz and it even ran some benchmarks but it would crash when running the Cinebench R11.5 benchmark. It would have been really cool for us to try and promote a 5ghz stable system, but sadly it was not to be.

To achieve this we set voltages to 1.45 and temperatures reached around 79c under extended load. Ambient room temperatures of around 25-26c were maintained.

This translates to around a 1.6ghz overclock when compared to the reference speeds – a staggering result and it shows just how capable the Noctua cooler really is.


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