1-Yes
2-The Voodoo 3 3000 will work on both 3.9 and 4.0
3-In 3.9 yes, in 4.0 no
5-No, it has no effects unless you use modern games that support AHI
6-The Radeon/Voodoo ram will be the slowest. You can use both rams and give them different priority (I would put radeon ram as low priority, in that way, it will be only used by the system if really needed)
