One thing I'd consider is that if you don't need the second Row Power 40, don't put it in. As long as your total current draw in the build is between 2/3rds to 3/4ths of the rated amperage of a single Row Power 40's rails, you'd probably be better off running the single power supply to both busboards. This also means there'll be less heat buildup in the case...and lots of heat + analog circuits = generally not so good, so if that's avoidable, definitely avoid it.