In a typical loop using a decent pump the water temperature doesn't change more than a single degree or two between hottest and coldest place of the loop.I never understood why one would want such a loop, hot -> hoter -> rad -> pump. I feel that in loops, hot -> rad -> hotter -> big_rad -> pump is a proper loop.
if you cite this
|Pump||XSPC Single 420 Bayres||Magicool MC-DCP450||XSPC Photon Laing D5|
|Flow Rate||7 Litres per minute||7.5 Litres per minute||20 Litres per minute|