Need help choosing RAM

[Aye]

I need help choosing RAM. I've used the RAM configurator for my motherboard and have narrowed it down to three choices. I want to know which 8GB kit is the fastest, overall.

1) F3-14900CL8D-8GBXM - 1866MHz - CL8-9-9-24

2) F3-17000CL9D-8GBXM - 2133MHz - CL9-11-10-28

3) F3-2400C11D-8GXM - 2400MHz - CL11-13-13-31

Obviously more MHz = faster but I'm unsure of the impact CAS latency has. Is a 2400MHz CL11 really faster than a 1866MHz CL8?

[emissary42]

1) F3-14900CL8D-8GBXM - 1866MHz - CL8-9-9-24
2) F3-17000CL9D-8GBXM - 2133MHz - CL9-11-10-28
3) F3-2400C11D-8GXM - 2400MHz - CL11-13-13-31

If you just want to get DDR3-2400 with no manual tweaking or overclocking get #3. I guess #3 is probably the cheapest option as well. However if you wouldn't mind overclocking you memory, #2 should also do DDR3-2400 with even better timings than #3.

Obviously more MHz = faster but I'm unsure of the impact CAS latency has. Is a 2400MHz CL11 really faster than a 1866MHz CL8?

Yes it is. Even DDR3-2000 CL7 can barely / can't match DDR3-2400 CL11/CL10 in terms of bandwidth. Also the F3-2400C11D-8GXM should be a double sided kit, so there is no rank interleaving performance penalty (that all the high speed kits using single sided Hynix MFR suffer from).

[Aye]

What if I wanted to go 16GB? 2x 8GB or 4x 4GB? Obviously higher density sticks will have higher latency. But is there any other performance/stability advantage between the two setups? I've read somewhere that it's better to stick with 2x 8GB but can't remember the reason why.

[emissary42]

Although the newer Intel platforms, because of their T-topology used for the memory slots, do a lot better with four modules than their predecessors, i'd still go with 2x8GB if you're not overclocking.

[Aye]

I'm not overclocking. And I just discovered my CPU cooler fan is blocking my first DIMM slot. So 2x sticks only. I don't know how I missed that..

Anyways, I've decided 2x 8GB is the way to go for future proofing. I've narrowed my choice down to this:

F3-2133C9D-16GXH - 2133MHz - CL9-11-11-31 @ 1.60v

Do you know if this is a double sided kit?

And thank you for all your expertise.

[emissary42]

As of now, all 8gb modules (2x8, 4x8 kits) are double sided.