Re: 4 GHz!!!
Zelda, I already have the most powerful single pump solution out there aside from the Iwaki RD30, and have already added another rad to my loop, and there are guys I've seen with noticeably better temps than me who are running separate loops to the CPU and graphics.
I don't think it's "inefficient" if you do it right; I'm not sure where you're getting that. Obviously, a CPU is going to heat up a lot less if you're not passing the water over two hot G80's before routing it back to it--not to mention adding all that extra tubing and restriction with two GPU blocks.
When I first constructed my loop I tested it before plugging in either of my GTX's. Temps on the processor were a good 7-8C lower than they are with them in my loop--and that's on all that additional tubing and restriction from the graphics blocks that wouldn't be there if I had the CPU on a single, short loop. That's a significant difference--especially when you begin pushing enough voltage to the processor to hit Intel's advisable stopping point for temps.
buffbiff also says above that the G80s added 6C to his temps. You just can't rid your loop of that extra heat/restriction/tubing.. no matter how strong a pump or radiator you have. Two loops is always going to get you better temps as long as you don't skimp on the parts.
i7-2700k @ 5.0 GHz
Nvidia GeForce 570 2.5GB Tri-SLI
Asus P67 WS Revolution (Tri-SLI)
OCZ Vertex SSD x 4 (Raid 5)
G.Skill 8GB DDR3 @ 1600MHz
PC Power & Cooling 950W PSU