Hi Andrew. Here are a few thoughts:
1. You absolutely want 1 micron or less for the bag. Small dust particles are the most damaging to the respiratory system.
2. Don't believe the published HP claims. Check the amperage, which is about 12 A per HP. Many companies, Grizzly among them, use "peak HP" for their claims, which is the power the motor can develop when not under load. Their systems have 6 to 8 amps per hp with 2/3 the advertised power. I went from a 2 HP Grizzly to a 2 HP Woodtech and the difference in power amazed me.
3. These things are very noisy. With an actual 2 hp setup, I found it possible to locate the vacuum on the other side of the wall in the laundry room and run the hose through the wall, add a remote starter and quick connectors on the equipment so just the hose connection moves from machine to machine.