One of the reasons why the ATR-42/72 turboprop airliners switched from four-blade propeller units to six-blade propeller units was the very fact this allows for slower fan blade speeds for the same thrust output, which 1) reduces noise quite a bit and 2) reduces fuel burn due to slower speed of the engine during flight. Why do you think Lockheed did the same thing with the C-130J, the current model of the famous Hercules cargo transport?
Hence the reason why the switch from eight-blade to ten-blade propfans. With more blades, this allows for slower blade spin speeds with all the benefits I mentioned above.
Apples and Oranges.
If you put on more blades and spun the prop slower, you may be quieter, but you also aren't going 450 mph anymore.