The converted to single pass rad does alter water VELOCITY, as you now have double the number of tubes carrying the flow. For RATE is however increased slightly due to the 4X lower resistence the rad should now give.
The question as to which is better in routing this set up is best answered with a question..
Which way results in the lowest number of fittings and the shortest lines with fewest tight bends in the lines? The answer of this question is also the answer as to which way is best.
I'd also strongly suggest you forget the NB block, they are a waste of flow rate. Not only does the block it's self impact flow rates, but the several tight bends required to route the lines to it will have a pretty large impact on flow rates. All these negatives for a block that will do NOTHING more than a Microcool or Swiftech active NB air cooler. So dropping the NB block will be the best thing I can see to do to insure best flow.
Best of luck!
