7-5 ...
Increasing the 5" to 7" is going to increase the air flow reaching those registers. Nobody should be worrying about velocity and noise on a 7" duct run reduced to 5" at the boot, at best it will improve the throw of the register. Increasing the boot may actually dimish the throw the 7" provides to the 5" ....
I would not worry about noise of 160 cfm @ an estimated 600 FPM, the old 5" under perfect conditions provided 70 cfm @ 500 FPM not a real noticable difference.... An improvement but nothing to worry about...
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