Lower CAS latency on a legacy Computer: Is it worth it?

Some Story background

With time going on, i got enough DDR2 modules to play a little with them.
An old question was how CAS latency is important and impacts performace on a legacy computer (with a CPU that doesn't feature any L3 cache)

Clock and CAS Latency
Modules used:

Name	PC2-	Frequency (MHz)	CAS latency	Size (MB) per module
Nanya NT2GT64U8HD0BY-AD	6400	800	6-6-6-18	2048
Corsair Value Select VS2GB800D2	6400	800	5-5-5-18	2048
Gskill Extrem2 PC6400PK	6400	800	4-4-4-12	1024
Gskill Extrem2 PC6400HZ	6400	800	4-4-4-12	512
Hynix HYMP564U64BP8-C4 AB-T	4200	533	4-4-4-12	512
Micron MT8HTF6464AY-53EB3	4200	533	4-4-4-12	512

only the green modules will be compared in this article, we'll play with the others later on.

Testing Conditions
Hardware & Software

CPU : AMD Athlon X2 64 5600+ (@2.9GHz)
MotherBoard:  Gigabyte GA-M61PME-S2P
RAM : Tested Criteria
GPU : Geforce 8400GS
HDD : Seagate Barracuda 7200.8 250 GB (7200rpm)
CD/DVD :  writer
Floppy

The Software used is nothing complicated: Memtest86 v4.20

Results
Single and Dual Channel CAS battle (DDR800)

Both Modules are 2GB DDR800 (PC2-6400), the only discriminating criteria is the Cas Latency : CL5 (5-5-5-18) vs CL6 (6-6-6-18)
Signle Channel (1*2GB) and Dual-Channel (2*2GB) results are the following:

• SC-5-5-5-18: 2369MB/s
• SC-6-6-6-18: 2252MB/s
• DC-5-5-5-18: 2861MB/s
• DC-6-6-6-18: 2643MB/s

Upgrading from ↓ to →	Single Channel 5-5-5-18	Dual Channel 5-5-5-18
Single Channel 6-6-6-18	+5 %
Dual Channel 6-6-6-18		+8 %

There is definitely a performance increase in pure RAM bandwidth, though this has barely any impact on real life work on a legacy PC.
NB: i also tried to mix the Corsair (5-5-5-18) and Nanya (6-6-6-18) modules, the motherboard set them to dual channel even though the chips are quite differents... and gave the following result:
It down-clocked the RAM to 667MHz (351MHz), and reduced latency to 5-5-5-15; for a 2410MB/s bandwidth.