What fans are you running on the BIX? Those have a high fin count IIRC and would really benefit from some 120x38MM fans for increased pressure.
I do not know what fans you are running already, but see 110CFm listed. And 120x25mm.
Another thing to consider is
CFM means nothing if it opts for the path of least resistance
Also shrouds tend to work best by getting a real one. The dead fan as spacer helps a little (eliminates the dead spot at the fan spindle) but a true shroud will open up even more area of the rad to be cooled.
I am no WC expert though.
Just out of curiosity.
You listed a dual loop res, and you are getting two pumps... what are you adding? what GPU i mean