Hi

This is a Catch 22 situation.

To use a RAM disk effectively for video editing and / or rendering, you need a computer running a 64 bit operating system with a very large amount of RAM which can hold the entire project video without resorting to disk swapping data in and out of the RAM drive to the hard drive - I would suggest you need at least 128 GB as a minimum.

Conversely, if you have a computer with a very large amount of RAM and a 64 bit operating system then you do not need to use a RAM disk, the software will use as much RAM as is available, and required, and disk swapping of data will be very much reduced, you can also do away with the Windows swap file which will make the OS faster.

If you want the maximum speed possible you have to find the bottlenecks in your system and eliminate them, the main one being using a single hard drive for both Windows and the data files used in the project. 

In my computer configuration I have one hard drive for the OS and programs, a second hard drive for all the data and a third hard (SSD) for rendering to, all drives are SATA 3 (6 GB/s) and my motherboard is a high performance model with an Intel generation 4 i5 processor and 32 GB of RAM. 

With this configuration, when rendering, the data bus, for any individual drive, has reduced alternation between reads and writes which slows thing down.

With this configuration I can achieve, for full HD (1920*1080) mp4, rendering speeds of ~ 54 fps ( < 1/2 x real time) on projects with one or two video tracks, and an audio track with mainly crossfades, cuts and fades through blacktransitions ,  down to ~ 25 fps on very complex sections of projects, eg with up to 21 tracks in use for collage effects etc.

For most projects, rendering takes less time than the actual length of the video.

HTH

John EB