[fhorst]

Looking good! I like your 2 big radiators! That should be able to kill all the heat in your system.

However, I do agree, the pumps should be paralel, as that will give a better head.
Serial as you have it now should in theory double the water flow (2 x 600L) at the same pressure. As the system is restrictive you won't get more flow. For that you need more pressure. So Pump1 -> Pump2 -> rad will give you more flow!

One other thing to consider, is that when you split the water at the radiators, the flow in the radiators will be half. (also the restricting factor) As it goes for your waterblock, more flow is better heat dissapation, the same goes for your radiator. With this in mind, you could also deside to go for pump - rad - pump -rad, or pump - pump - rad - rad.

As you already have big radiators, the temp change won't be that much. As you go closer to ambient temp, it get's harder to get the last degree out of the water. (it's mre easy for a rad to cool water of 40c to 30c at 20c ambient, then it is to cool water from 30c to 20c at 20c ambient)

Let us know how it cools!