Need help deciding on dust collection strategy

I know this topic has come up a lot and I read most of the threads on here on the topic. Still, I'm undecided. My shop is 600sf (20x30). I'm a hobby woodworker and have the. HF dust collector in one corner. I intend to upgrade the impeller on the HF unit to the Rikon part.

The tools I have right now are an old Delta unisaw, an 8" Delta joiner, a radial arm saw, a 13' thickness planer, an old Delta/RW lathe and a small drill press station. I ran 4" PVC under the concrete from one side to the center for use by the tables. I have put a drop ceiling in with troffer lights and will be installing batt insulation and ceiling tiles so the space will be constantly heated and cooled.

What I am undecided on is to use either 5" metal duct for my main trunk lines or use 6" metal/pvc. My local hardware shop has 6" pvc drain pipe. I have both 5" and 6" metal duct. My longest horizontal run is about 25ft.

My two approach ares:

a) 5" mains using wyes that I fabricate myself (already done done) or order (sheet metal kid) with 4/5" drops too tools. The reasons to do this is because it likely will have higher air speed.

b) 6" mains using metal duct or pvc. 6" parts are more readily available. If I decide to go with 6" then I would enlarge the inlet on the HF unit to 6". The main I can think of doing this is so I can upgrade my DC to a 3HP unit later on and not have to dig into my ceiling to replace the 5" pipe to 6". I know 5" pipe can work with 3HP unit as well but 6 would be better. I prefer to use PVC simply because it's easier to work with but metal is ok too.

I just don't know if the HF unit with the upgraded impeller can keep the air speed up high enough in the 6" duct. I see people on Youtube that say yes, but just not sure.

Whatever I decide I will be running my mains above my drop ceiling so I really don't want to be digging into my ceiling for any "cleanup" work. I will be either building or buying a cyclone.

Any advice welcome!