It depends on how much RAM you have. If you have say 2TB of RAM, it should make things faster, although copying the file system to it and then doing redirection might be an issue.
Could antivirus APIs be used in a program to detect changes to the disk while it copies things to the RAM drive? Could a junction point be used afterward to do redirection? When you want to shut down the system, could the changes be merged back into the
filesystem without causing problems as it is done? These questions probably need to be answered before doing this kind of thing.
No, it won't ever be faster. All you do is remove RAM from the amount of usable memory and introduce unnecessary copying between one bit of RAM (the ramdisk) and another (the filesystem cache). This never works out quicker. Ever.
The reason the ramdisk exists is to fake storage when it doesn't exist. In an embedded system, for example, the OS might be permenantly stored in a ROM, but you might need to run an application that expects to be able to write temporary files to disk. That's
when you use a ramdisk. It's nothing to do with improving performance.