From what I've read so far, it isn't absolutely necessary to cool the SB on our board, so one can leave that out of the loop to keep the water heat and costs down.
As a temporary fix, have you tried a 40mm fan screwed to your northbridge heatsink? I did that and it made a noticeable difference in stability.
I'm thinking I might risk CPU, NB and GTX in one loop, and sort out a replacement passive cooler for the left bank of mosfets, and see how that goes.
I know given the hot parts in the loop it isn't ideal for mega overclocks, but hopefully it should provide a half decent o/c quietly...
I had a AMD sandy 3700+ @ 2.8ghz, DFI chipset and X800XT all on the same loop. As I sold each block I was finnaly left with the cpu only being cooled, the temps didnt change. The Gfx card was below the temp of my CPU and the chipset was also around the same temp as my CPU, it made no difference.
Now, I dont know what temps the chipsets get to on these boards so its hard to tell, but You may get away with the GFX card in the same loop as the CPU as long as the card is the same or below the CPU temp. I dont know if it realy works out this way but it sure did look this way on my last set up.
When you say it made your system more stable with the 40mm fan, did you mean you could clock higher than without it? My system is 100% stable at 3ghz. Unless I can jump to at least 3.4ghz I dont think id notice the difference to warrent the extra noise.