I know it is probably too late, but I have the chiller you posted in your original post. Does great when ground water gets to 50 degrees but with summer water temps it must be run painfully slowly to cool to pitching temps in one pass. I read that the number of plates just helps flow and that you really want longer to increase the temperature drop. If I had to do it again (when I have to do it again) I will get something like this - http://www.dudadiesel.com/choose_item.php?id=HX2330BWGH
I think dudadeisel actually makes the one that Austin homebrew sells (at least the smaller models on the site look exactly like what I got from AHS) being in TX I would think you would want more capacity.