Higher memory clock leads to performance drop

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I've been tweaking my system to see how far I can push various bits and was
more than a little surprised to find that under certain circumstances
dropping my memory clock increases performance.  I'm curious to find out

ASUS A8N-SLI Premium; Rev 1.02; BIOS 10011-005
AMD 64 S939 X2 4200+
2 x TWINX1024-3200CL2 (= 4 x 512MB)

FSB freq: 240Mhz
CPU multiplier: 11
Core speed: 2640Mhz
HT: x4 = 960Mhz
Mem Timings: 2.5-3-3-6-2T

PCMark05 Test 1:
Mem clock: 400Mhz x FSB = 480Mhz
DDR voltage: 2.75
PCMark05 score: 5479

PCMark05 Test 2:
Mem clock: 333Mhz x FSB = 398Mhz
DDR voltage: 2.70
PCMark05 score: 5780

The difference between 5780 and 5479 is too great to be explained away by
normal margin for error.  A look at the test details shows that for the
first test the memory latency (Random 16MB test) was 11.216 MAccesses/s but
on the second test it was 10.196 MAccesses/s and my guess is that's
impacting on the other memory-bound tests.  I have run these tests more than
once and the results are consistent.  It's most intriguing.

Re: Higher memory clock leads to performance drop

I also saw while manually overclocking that my overall score was dropping. I
let my memory run from 403 upto 418. What I did instead was enabled the High
Performance setting in the bios and my overall score went back to 1398 from
1360 and my cpu score jumped up to 4800 from 4412. With manual overclocking,
I didn't get higher than 4600. The high performance setting has my processor
clocked at 2.29 ghz from stock 2.21. I'm wondering if PC3500 or higher
memory was used, if these scores would increase. We're both using pc3200,
which could explain this.

Gigabyte GA-K8NSC-939, A64 3500+
2 Gig Dual Channel OCZ PC3200 Platinum Edition XTC 2-3-2-5 CL2.5
ATI All-In-Wonder 9600 XT
WD120gb + 80gb HD 8mb buffers
Liteon 1693S 16X Dual Layer
Pioneer DVR-110D 16X Dual Layer
ViewSonic 19" A91f+ CRT
Micrsoft Sidewinder Precision 2 Joystick

Overall Score 3DMark05 Free- 1398 CpuScore-4822
Overall Score 3DMark2001SE- 12429

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Re: Higher memory clock leads to performance drop

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I'm still investigating.

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