Unexpected results - higher flow = higher temps

[virtualrain]

I have an interesting observation and I would like your thoughts...

My temps are higher at high flow rates and slightly lower (but certainly not worse) at lower flow rates.

Loop:

DDC Ultra w/mod /res > DDC Ultra (stock) > BI GTS 240 > BI GTS 240 > Apogee > MCW30 > Alphacool watercooled PSU

Note: I'm not yet watercooling my GPU.

I use a pair of 140mm SL Yate Loon fans on EACH rad (4 fans total). They run at 800 RPM.

I have an Aquaero and use that plus a couple of these circuits to vary the voltage to the pumps from 7V to 12V...
http://home.nc.rr.com/katyandrandy/pwm.htm

The following temps were noted after running dual Orthos Prime for 1hr. on separate days.

At 12V the flow is about 6lpm and temps are:
Room Temp: 21
Water in: 29.7
Water out: 29.5
IHS: 27.8 (thermal probe on side of IHS)
Core: 43 (as reported by Speedfan)
CPU: 44 (as reported by Spedfan)

At 7V the flow is about 3.5lpm and temps are:
Room Temp: 22
Water In: 29
Water Out: 29
IHS: 27.1
Core: 40
CPU: 43

Why would my temps be the same or lower with lower flow? I would have expected worse temps with lower flow.

I assume this means that the cooling effectiveness of my rad/fan combo cannot benefit from higher flow. Is it that the water is moving to quickly through the rads to be effectively cooled?

I assume more airflow and/or better rads would change this so that temps would decrease with higher flow?

I guess one other observation from this is given my system design, dual DDC's is really not helping.

When I get my graphics card in the loop, I suspect I should also look at upgrading my fans from 140mm SL's to ML's to move more air?

I'm interested in your thoughts.

EDIT/UPDATE: After input from a lot of people, I think the link in Post #30 provided by fairydust answers the question as to why more pump is not always better! Here's a review that anyone considering dual pumps should read!

Update: Added some photos.

Here's a few notes that will make the photos make a bit more sense...

- I originally fitted everything using a wooden MDF mockup of my mobo and expansion cards. At the time I was hoping to cool the GPU as well as the chipset but given the layout of the Mobo and other constraints of my design (namely the rads on the side door) could not cool both the GPU and chipset. Knowing I would soon be updating to a Conroe and G80, I decided to wait on the GPU cooling. At any rate, in one of the pics you can still see the wooden computer mockup with GPU block on it.

- All tubing is 7/16" Masterkleer with coolsleeves. The tubing connecting the rad to pump 2 at the top and the CPU block at the bottom obviously had to be given a lot of thought so the door could be opened and closed without kinking the tubing.

- Flow basically starts at the top of the chassis, flows through the rads and then works its way back to the top through the blocks.

- In the top of the chassis at the rear is the water cooled PSU which is the last water block in the chain. That feeds a small DD fillport res which then feeds the inline Remag flow meter before Pump 1 which has the Alphacool res which is mounted in the top front bays. Pump 1 then feeds Pump 2 which is mounted under the blowhole near the res. This then feeds the rad inlet.

- The DD Fillport res made bleeding a lot easier than useing a T. Trying to bleed using a T with dual DDC pumps is not practical. In fact, I had to glue some fish tank sponge to the top of the res to trap air so it would not get sucked back into the loop. I found that with dual pumps any air in the loop or the T will get sucked into the loop.