halfblazed :
Pmp>CPU>Radiator>Reservoir
I have always heard that its best to have the CPU block directly after the pump so that it gets the most pressure. However, it probably won't make a noticeable difference.
I would say make the "Order of Flow" have as little tubing as possible. The shorter the loop is the faster the coolant can make its way through all of the components.
After looking at pictures of your setup, (nice looking by the way!), your flow order is actually, Pmp>Memory>CPU>Rad1>GPUs>Rad2>Res
You actually have your memory block in line before the CPU.
You actually break, your quote:
"I have always heard that its best to have the CPU block directly after the pump so that it gets the most pressure."
Obviously you think cooling performance wise, pressure is more important than the actual water temperature?
Where exactly did you get this information from?
I would think if you are running a pump powerful enough to do the job in the first place, pressure would be your last concern, getting the coolest water to what you are actually cooling, would be my highest concern for the best cooling performance possible.
Obviously very few seem to share my views regarding this subject, but I still stand that the best cooling performance, is to have the CPU immediately after the radiators seeing as how the CPU needs as much cooling as possible, especially since you are overclocking your CPU to 4.5ghz.
GPUs are much more temperature forgiving than an overclocked 2600K is.
As I've already said, "Your rig is very nice looking", you put a lot of work into it and it's obvious, I additionally am saying that you could improve it's cooling performance rethinking and rerouting your flow order.