slicedtoad :
4Ryan6 :
If you're after CPU cooling performance you'd want to push through both rads then to the CPU and take advantage of their combined cooling capabilities to deliver to the CPU water block.
Especially with overclocking in the picture which I know you do, you need all the cooling you can get delivered to the CPU from the combined radiator cooling, it's like using one radiator as a pre-cooler usually the lesser rad, and the second for the main cooling before the CPU.
How you set up that loop has everything to do with end results unless cooling performance is irrelevant.
But there's only one block in that loop, does it really make a difference what order the loop is? The water always goes through two rads between cpu passes, regardless of order. Since nothing else produces heat (except a tiny amount at the pump) why would it matter where the rads are?
Maybe I'm missing something but that doesn't quite make sense to me.
The only cooling elements you have in a loop are the radiator or radiators.
The reservoir is the recovery component that collects and stores the coolant to always supply an even flow of coolant to the pump, it has no cooling capability by itself.
The pump circulates the coolant through the system and to a very small extent is a heat producer from the motor windings heating from voltage flowing through them, so the pump can benefit from cooling as well, but the pump does not need the most cooling.
The water blocks are heat conduction transfer elements to the water from either the CPU or GPU, so the cooler the coolant is when reaching them the cooler they can cool the component.
No matter how many radiators are in a loop, for best performance cooling they should be in series just before the CPU or GPU being cooled, the coldest coolant is exiting the last radiator.
The radiators looped in series progressively aid each other lowering the heat, they are pre-coolers each lowering the temperature a little more before it reaches the water block.
Many in the water cooling community do not water cool for cooling performance, they water cool for looks, they water cool because they can and various other reasons, and many don't even overclock at all.
I water cool for overclocking performance cooling period, I have no other reasons and have tested myself to discover the maximum cooling I could get from what I have invested my money in.
The coolest dependable coolant temperature is leaving the radiator that's an undeniable fact, so if you have one radiator or ten, they should all be in series before the intended to be cooled component.
When overclocking is brought into the picture it produces and extra heat load that IMO is what water cooling is all about, there is a difference regarding cooling performance sometimes as much as 3c ~ 5c in the way the water cooling loop is setup, but even if it was only a 1c solid gain by simply the routing it would be worth it regarding cooling performance.
In all honesty this is not rocket science, just logically looking at a radiator cooling loop should turn on the light bulb in the brain, but if that doesn't then try it yourself with comparative before and after temperatures, it's just a simple tubing reroute, tubing should have been your cheapest water cooling expense.
Radiator water cooling is totally at the mercy of ambient room temperature no matter how much radiator fin cooling area you have, you will never do any better than ambient, if your total cooling area is from multiple radiators, they need to be all working together to cool the intended component.