I use the Zalman CNPS20LQ with 2x Corsair SP120 for a push pull and I must say it is more efficient and quiet than my old Zalman CNPS9900MAX. DO NOT got with Corsair, as their pumps are noisy! Had tried a H100 (Corsair's own custom pump design) and H110 (using the Asetek reference design) and both pumps got real loud after 1 days use. Interestingly enough, the H110's pump is the exact same design as my 20LQ, however it ran 2000RPM faster! Compared to the 20LQ, the H110 was a mere 1'C cooler under load.
I will highly recommend AIOLQ over air any day. I agree, AIOLQ are slightly more/less efficient than the best air coolers, depending on the CPU, case, and of course SIZE; your results will vary. However the tradeoffs are well worth the "potential" difference in price; Space/size, noise, cool factor (literal and figurative), and the ability to swap out the fans at any time. As well, quite a bit less stress on the mainboard's pcb!
Right now, my room sits at 21.5'C ambient, and @ 1.60GHz 0.86V my 3770K is idling at 16'C with the all case fans set to min rpm. Under load I never exceed 60'C, and I have a ****ty hot, average silicon yield 3770K. In the BIOS, the CPU sits at 3.5GHz 1.24V and the CPU reads 22'C. That my friend is fantastic cooling!
If one wants to try this, and I warn you to use caution if doing so, plug in an uninstalled AIOLQ and feel the radiator and the copper cpu plate. They get extremely cold. The rad alone gets so cold that it is difficult to hold. The cpu plate, and this is where you use cation, gets so cold I got scared my finger would freeze to the copper I yanked it away.