Ear muffs loud and there is a wall between me and the DC. A pure dB level as advertised is not really relevant. Your perception depends on the spectrum. A rating can play games depending on the weighting scale. Now, as I know a bit about acoustics ( built high end loudspeakers for many years) I do intent to attack the noise level. Mine sits in a corner with hard walls all around. The worst configuration for sound.
There ate two ways to make the system quieter. The first is muffle. Mufflers, regardless of technology and all the ads for magic hot rod mufflers, reduce the efficiency. Just physics. You can muffle by restriction or by absorption. Both reduce flow. Sorry. Or, you can be more careful in design. Things like carefully spaced notches on the impellor so the trailing edge vortices harmonics to not complement. ( not seen one on a DC) Good attention to every edge and transition. CV is not the best in how their plastic is overlapped. How you duct corners, junctions, gates and basically everything in the flow is implemented. I have not seen how Harvey deals with these issues, but they claim lower noise. However, they have lower flow.
I kind of doubt the 5 HP CV is not as strong as the 3 HP Oneida. Nothing against them, but there are so many ways to tell the truth, but tell a different story it is hard to compare on paper. Oneida is fully respectable, but they are in competition! ( notice the CV is not in their comparison chart), but it is a 5 HP) You would have to hook both units up on a representation of your ductwork and tools and measure the airflow and lift. They would likely be different, but which best meets your requirements is an unknown. Don't know what that "boost" is. To split the flow you use a "Y" and gates. CV has an option for a slightly larger impellor.
Again, there is nothing more expensive than buying the wrong tool. My single stage bag, then converted to media filters, was a total waste of money as I still had to buy the CV and re-duct a third time.
Just to keep you confused, I have never heard owners of either CV or Oneida be unhappy or identify a major flaw. It is my belief the biggest problem is not a DC big enough, but the horrible design of tools. Knowing a little about fluid dynamics from studying automotive intake and exhaust systems, it is clear that engineering topic has not reached tool designers. Take the lower 4 inch port in my Harvey band saw. A big grate in it and square edges on the inside. Doing rough calculations ( real ones are really really hard) it is about as effective as a 1 inch port with the proper flair. In other words, pretty useless. The upper port opens to basically free air with nothing to pull across the band gullets. The big 6 inch port into my table saw is pulling from a low pressure plenum. Again, nothing to push the dust from the blade gullets so it carries them around and flings them out the top.
Some folks like the steel of the Oneida. Easier to ground, but I found a couple turns of copper wire around my cyclone does a decent job of draining the static. Without it, I did blow up two infrared bin full detectors. Inadequate design of the sensor as it was not "suitable for use case", but that's a different story.
Folks remember, the reason for a two stage is to force out all the fine (dangerous) dust before it gets to the HEPA filer. If you don't, then the single stage will work as well as the two, for about 5 minutes. After that, the filters clog and performance drops like a rock. The better the cyclone, the less fines make it to the filter canister. You do get some loss on a two stage over the identical
clean single stage. Is the fine dust that important? Well, I bought my drill press from the widow of a woodworker who did not have a DC system. Emphysema. Non-smoker. Proof? Of course not, but a darn good hint!
OK, it is time for a pint of Gaelic ale. Enough blabber.