The kingwins LZPs are great (haven't tried AP). I have a 650 and an 850. After seeing mines, 3 friends have also gotten one (1 650 and 2 850). The fan doesn't kick on till you are over 500w and there is zero whine (I am VERY sensitive to high pitch noises).
I thought in a close loops, gravity was irrelevant (well 99%). This is due to the fact that when the loop is filled, the pump pushs water and 1 direction, while the negative force behind the pump pulls the water to neutralize itself.
Don't really like how I worded that, but I believe, but I...