Personally I'm not looking for "the lowest temp", I'm looking for stable temp, I'm not worried about a few degrees hotter, it isn't gonna do much for me, I rather go for the clean look... I always ask, is a few degrees really that important to you? Since you're water cooling, not that important...
Depend on your cpu, my i3 is rated 65c while my gpu rated 100c, I run my loop to gpu first then to cpu, i never see higher than 45c, this is using only 160mm + 120mm rad