For the same price: 1066Mhz CL5 or 800Mhz CL4 for gaming?

[LodeHacker]

Hi!

I am going to replace my current RAM sticks (Kingston ValueRAM, 4x512MB 667Mhz CL5) with high end Kingston HyperX memory (for my new 2009 gaming build). I am going to overclock the whole rig to a new level (got my salary finally, will get a Core 2 Extreme Quad too and a liquid cooling kit).

I am not sure about which RAM to get, I have heard that CAS Latency is a much more important number than the Mhz of RAM. However the difference in speed of the two memory modules is 266Mhz.

For gaming / overclocking, would a 1066Mhz CL5 RAM stick give better performance versus 800Mhz CL4 RAM? I have checked the Qualified Vendors List for my ASUS board and both types of Kingston HyperX memory are on the list, so I can be assured they work no problem. It's the CAS Latency that makes me tick my head. Previously I've always bought CL5 memory because it was cheaper, but now for the same money I could get faster memory (more Mhz) or lower latency (less CAS Latency).

Thanks in advance!

[angelkiller]

Honestly, only benchmarks can show the differences in memory speeds/latencies. You'll never notice the difference between DDR2-533 and DDR3-1800 in everyday applications.

That said, I'd get the DDR2-1066 modules because they can underclock to DDR2-800 CL4, and (most likely) OC farther than the DDR2-800 could.

[LodeHacker]

You just said I could underclock memory and have lower latency. Is it really possible to underclock a CL5 module to have CL4 timings?

[QuietOC]

I am going to overclock the whole rig to a new level (got my salary finally, will get a Core 2 Extreme Quad too and a liquid cooling kit).

To get some real benefit you need to use the 1:1 memory divider and match FSB to memory speed. Up to 400MHz FSB (1600) DDR2 800 is best. You would need the FSB up to 533MHz (FSB 2133) to max out DDR2 1066.

Cheap 1.8V DDR2 800 CL5 is fine--"faster" DDR2 is just the same chips overvolted/overclocked--I wouldn't pay more for it.

[jhhoffma]

Yep, remember that the CAS latencies are measured in clock cycles. So a 1066MHz clock module with CAS=5 is still faster than a 800MHz chip with CAS=4.

Try this:
CAS * (1/frequency) = (# clock delays) * (time per clock) = total CAS delay (sec)

So for 800MHz with CAS4 we get:

4* (1/800) = 4 * 0.00125 = 0.005 sec.

But for 1066MHz with CAS5 we get:

5 * (1/1066) = 5 * 0.00094 = 0.0047 sec

So the 1066MHz with CAS5 is still theoretically faster, but then you have to worry about matching FSBs and all that so you end up with a wash. In reality you would want the lowest latency period, but I would second what angelkiller said about buying the 1066 and running it slower. Especially if it comes with some decent memory sinks.

[LodeHacker]

If that's the case I'll go with the 1066Mhz modules then. I looked at some other forum threads about this and found out with 1066Mhz modules read times are better (=faster). So running 1066Mhz modules slower... I know it sounds dumb but will they produce more heat or less? I know that overclocking a CPU makes it get hotter, but never tried to underclock something. I'm not the overclocking expert, but have clocked a bit so I know the basics.

[QuietOC]

So running 1066Mhz modules slower... I know it sounds dumb but will they produce more heat or less?

Less, but lowering voltage lowers power consumption more.

Actual memory latencies (in seconds) haven't changed much since DDR:

DDR 400 CL2, CL2.5, CL3
DDR2 800 CL4, CL5, CL6
DDR3 1600 CL8, CL10, CL12

Those are all the same latency top to bottom in seconds. The timings on the left generally require more voltage.

[LodeHacker]

A quick look at the Kingston website reveals that the 800Mhz CL4 variant requires 2.0V and the 1066Mhz CL5 modules 2.2V. At another forum I read that the more volts a memory module needs the more likely it is overclocked RAM. So in this perspective isn't the 800Mhz CL4 module higher in quality? Like I said I never worked before with other modules than CL5 so the volt thing is keeping me to think if I should go with 800Mhz CL4 instead. Even if the rig gets OC'd pretty high I am going to use the best possible components to keep the heat levels low. That's why I'll combine liquid cooling with some pretty Nexus fans. In terms of stability which modules would you buy?

[QuietOC]

I haven't seen true CL4 1.8V DDR2 800. G.Skill has some 1.8-1.9V CL4 DDR2 800. Mushkin has 1.8V DDR2 800 5-4-4-12 modules. The Mushkins are probably worth something over generic CL5 DDR2 800, and the price isn't bad either.