The speed of transfer doesn't correlate to more FPS is what people are telling you. It will certainly improve load times to some degree (though usually loading is done in parallel with some processing), and for games that load content dynamically, it will prevent jitters from occurring if things are loaded at time of need.
It won't increase FPS, just the same way an SSD doesn't increase your FPS when compared to an HDD.
All important data is *usually* loaded in RAM at load time from the hard drive (exceptions to this are common, but the implementations is usually such that you don't often hit a situation where the content you need hasn't been loaded yet) that is why storage speed, while important for a satisfying computer experience, is not critical to FPS.
The big turnoff for RAMdisks is the management overhead, since you have to do some setup every power up. If you don't mind that setup, there are probably cases where it really pays off. I personally, would consider it for RPGs where frequent long load times are common (such as dragon age, witcher, etc); if you can cut a 45sec load time to 3 or 4 seconds every time you open a door, it's worth 5 minutes of setup each time you want to play the game. However in a multiplayer game, where loading faster just means you get to wait longer for the match to start, what's the rush...