bigben2k, right now the only coolant i'll be using is water... but that's a coolant, just making sure we were on the same page.
It makes sense that the higher PSI models can reach a higher head height...
i thought the PSI level was always at whatever level the pump's rating was, but i think that's just the max PSI the pump can exert, which makes sense.
With my showerhead, that's adding an lot of 'head' to the setup, so i need high PSI to get good flow through the showerhead.
Also, this will make more mist, as you pointed out decodeddiesel.
FYI, here is a great reference w/ many pump specs of many pumps:
http://www.petsolutions.com/Wpumpchart.html