My guess is you'd be better off running both pumps in series on one loop (they are apparently not wildly mismatched as regards max flow rates)
You gain more by increasing flow through the wbs than through the rad...
pump + wb specs?
Lots of discussion around this idea (+not much hard evidence)
http://forums.procooling.com/vbb/sho...ight=dual+pump
http://forums.procooling.com/vbb/sho...ight=dual+loop
http://www.ocforums.com/showthread.p...0&pagenumber=1