A question about these 2 pumps

MD40RLT
http://www.marinedepot.com/md_viewI...dproduct=IK1143

MD20RZT
http://reefs.org/library/pumps/pumps/iwaki20rzt.html

The 40RLT shows 21.3 Max Head while the 20RZT shows 24 Max Head... but the 40RLT has a 750 GPH @ 4' Head and the 20RZT has 210 GPH @ 0' Feet.

I'm not exactly sure what all that means especially since one is at 4' and the other at 0' but would the 40RLT be a better pump... slightly less Max Head but it looks like it has more GPH... I may not understand all the specs though so tell me if im wrong.

Which do you think would be better?

Poo? Anyone got any ideas?

The MD 20RZ will be the best of those two by a ways. It has more head and less or the same amount of heat added to the water.