a problem that i already pointed out in a thread of its own.
parallel, pressure won't drop more (in the WB) than it would drop from a serial setup. however, you will need quite a stronger pump to prime the air out of the rads than with a serial setup.
temp wise i haven't been able to measure this.
the situation was
maze2 / 2hc's / 1048 in serial setup i would get a certain temp result of the cpu
trying those same components parallel didn't yield ANY measurable temp advantage; however the tubing that exited my rads and was going down to the res had these big bubbles that didn't get blown to the res
i changed that setup to a 1250 pump, (set me back 100$) and the bubbles got blown out nicely, but i didn't get a temp improvement.
that leads me to my conclusion that if u can get the setup routed shorter and more conveniently serial then you will almost always be able to get away with smaller pump and get the same temp results. ofcourse nikshub will not be having that problem, since, if i recall well, he has an iwaki superhead pump.
edit: here's the thread i once started about the serial parallel enigma:
http://forums.procooling.com/vbb/sho...erial+parallel