Unless you have a hard drive failing or Minecraft doesn't have proper RAM allocated to its java VM, a Ramdisk will provide zero impact on framerate. And if you think it does, it only reveals a severe lack of a basic understanding of whats going on. A Ramdisk is great for things that are accessed a lot (servers with large worlds and several players). With client/SSP Minecraft, this is not the case. You have a tiny application, that creates a very large 3D world. That process takes up a lot of RAM, but the RAM that takes up is not stored on the RAM drive. The ramdrive in this case is accessed to retrieve small bits of data. A couple MB worth of class files, PNGs, .OGG media, dependencies as well as very slowly fed your game world. (we are talking about client or SSP here, not server) Even the slowest (new) HDD (let alone SSD) drive you can buy today (this includes data throughput and IOPS) would take less than one second to load minecraft in its entirety (plus dynamically accessed world data if applicable) into ram for processing.
Make sure your hard drive isnt failing and you have jvm ram allocation set up correctly (~2gb for ftb with far) or you will see major stuttering as the computer access the VM. If you put Minecraft on a working system and its set up correctly, and then you put it on a ramdisk, you will see zero framerate difference. So putting it on a ramdisk does not impact it unless there is another issue, and you end up not really fixing the main problem.
TLDR: The ramdisk itself is not used for rendering and therefor has zero impact on general game performance unless your drive is failing or it was accessing the VM due to bad settings (this isnt fixed by going to a ramdrive, your settings changed by coincidence in your favor).
Correlation does not imply causation. Stop giving bad advice.