In my experience, the order of the loop doesn't matter at all.
Water can pass through a rad with minimal temperature drop and pass through a block with minimal temp gain because water is moving so fast. I am not sure about a restrictive loop though but if water is moving fast enough. You won't need to worry order.
I tried organising my loop which uses a MCP 655 w/ EK top and it doesn't make any difference between may parts which include vid card, CPU, NB, and dual thickness rad. Temperatures seem more or less the same despite the configuration. The largest change I seen was 1C difference. I would work towards a less restrictive loop.