The stock cast hub is actually two peices... the outer aluminum drum and a steel hub that are seperated by cush-drive rubbers. There's no problen going to a billet hub. You do lose the cush-drive which is supposed to help with wear on the driveline. The weight savings of the billet hub will be negligible, but the posts should be stronger than the cast unit.
The OEM cast unit is two-peice w/ cush drive. I dont think I've seen an aftermarket cast hub before, but they may exist. I honestly couldnt tell you how much wear and tear the cush drive will save you, but it's OEM for a reason
Unless you are racing it and are concerned with every last ounce go with the stock style hub. The cush in the stock hub protects the trans gears from high shock loads which can cause pitting on the gear teeth and/or shear the teeth off. Most of the time the spring stands shear off because the stand has suffered some sort of impact usually in the form of contact with asphalt.Using one of the aftermarket pressure plates that are thicker and protect the spring and stand is cheap insurance to keep it from happening again.
For the street...Always go with all cushes in the drive.
Had a Guzzi rear wheel cush sieze and the clutch splines ate-up in 20k miles.
Early HD Sportsters had NO cush in the drive system and will eat chains alive!
Some bikes have three cushes in the drive.
One in the primary, like your clutch hub.
Another in the rear wheel hub and some even have a cush system in the trans, like Guzzi & some BMWs.