The cpu block should be the first part in the loop followed by the video card then it would go to the resivoir and then to the pump and then to the radiator and out of the radiator into the cpu block.
I think that the resivoir , pump and radiator can be in any order but the cpu has to be the first block to be connected in the loop.
I have the blocks connected and then it goes to the radiator , to the resivoir and then the pump and out of the pump into the cpu block.
I just noticed that you had two radiators? The 360mm should take care of the cpu and video card without any problems but if you already have them you could put the 240mm in between the cpu block and the video card block , you'll just have a lot of tubing running around your case.
I can confirm what jacknhut said about the slightly lower temp when you put the CPU in the loop right after the radiator, especially when you have 2 video cards in the loop also. When I put the CPU after the 2 video cards in the loop, the CPU temperature is usually 2-3C higher as compared to putting the CPU right after the radiator in the loop.
Loop order does matter , I want my cpu to be the first block to be hit after the radiator. Because the cpu , more than video cards is overclocked and needs the heat to be dissapated. If I'm using two video cards then I'm going with two loops so that both the video cards and the cpu will be first after the radiator.
It's typically less than 1-3C at any single point in the loop, but this depends on loop delta (which includes ambient temps, total heat output in watts, and flow rate...along with other items). The thermal conductivity and specific heat of water is very good which means it has the ability to quickly absorb and dissipate heat energy as well as absorb a high amount before the water temperature actually changes.
Water temperature of your loop is not the same as the reported temps from hardware monitoring solutions. Loop Delta-T is a combination of several factors and what you should be most concerned with.
The pump/res placement is more or less irrelevant, though convention puts it before the cpu, for ease of tubing I've seen loops start with the gpu without issue.
The only thing I'd try to make sure of, is that you have a radiator inbetween each of the components. That way hot water from the cpu won't be fed directly into the gpu (or vica versa). I played around with my setup, and there really is a 2-3 degree difference. You'd be better off just doing whatever keeps the tubing routes cleanest/shortest.
If thats true I've love to see some screen shots since its hard to believe he has less than 1 C load temp difference between his CPU and 2 GPUs assuming its a serial loop. Also, in order to achieve that, his CPU waterblock must be incredible efficient or his GPU block must be so bad that the CPu and GPUs temps are the same since CPU is usually a lot warmer than GPU in watercooling no matter how much radiator space you got unless you got sub ambient watercooling.