I'd get dual loops if it fits your budget. IMHO the NB and the SB needn't to be cooled. They should only be cooled for heavy overclocking purposes. So if I were you I'd get the CPU in one loop and the GPU in the other loop.
Ah... I see. The main reason I want to watercool my NB and SB is because I want to get rid of that noisy fan on the chipset for the 680i.. If I don't water cool them, can you recommend a good aftermarket chipset cooler for me?
NP, NCIX has plenty of NB and SB coolers around there. I recommend the one on the bottom, refer to Terrence J's review at the bottom. Since the cooler is passive it will make NO noise. BTW, if you want you can add a 80mm fan.
Ohh and I've been looking at Xtreme Systems lately and I saw some pics of people's WBs and res and stuff all messed up because they did not flush out their rads, more specifically, the PA120.3. Would the same happen with a MCR220?