About RamDisk and RAID0

How much time will it take to load into the RAMDisk?

roughly 50 seconds.

And if i buy a seccond 840 and install it in RAID0, will it cut the time it takes in half?

Yes but its not worth it.(Explanation later)

Would i notice the difference between playing of a 2x840 256GB in RAID0, and playing off a RAMDisk ?

Only when the program starts.

(How ram functions for gaming)

When you run a game, it loads the game(engine) into the ram and the initial loading screen is pretty much all the libraries the game is loading into ram so it may run. Once its loaded into ram, CPU, ram speeds, and Graphic card are the major affector to the games running speed. When the game does a map change, it had to load the map from the hard drive into the ram which is why in BF4, there is a 1-2 minute loading time for maps.

(How does ramdisk help this? (NOT FIX))

Ramdisk is when you create a virtual hard drive inside your ram. By doing so, you can load your program directly into the ram before running it. When you go to run it, its transferring the game files from a virtual disk(inside the ram) into the ram locations for running applications. Ram has a massive transfer rate compared to HDD/SSD meaning loading times, and map load times are drastically reduced.

(Problem with ramdisk)

Ram is called Random Access Memory for a reason. It is one of the most violate memory solutions for computing and is the most violate widely used solutions in current use. Ram is usually one of the first thing to cause problems with your computer which is why good ram can get quite expensive.

Try to refrain from games that try to save locally as they may accidentally corrupt the data. games like BF4, and many mmorpgs work wonders because everything is processed and stored on a dedicated server.

(Why Raid0 shouldn't be used with a ramdisk)
Once a game is transferred onto a ramdisk virtual drive, the game will load, run, and save to that virtual drive so your HDD/SSD raid won't be doing anything after the game is transferred.

(Better solution)
Instead of storing games on a SSD, store them on a HDD. Personally my dream rig has multi terabyte hard drives configured to auto load my games to the ramdisk. Although this means the game takes longer to start due to transferring files to ramdisk then running. My game will run the same once loaded into the ramdisk as storing on a SSD and i gain the ability to have many more games available.

(Lastly)
Shop around for the proper ramdisk if you decide to buy one. Most only create the virtual drive on the ram. A few will actually give you the ability to convert a folder into a ramdisk prebuilt disk (much like a virtual dvd) and you just mount it through the ramdisk menu. This makes it easy because you tell a game to mount, get a cup of coffee, go feed the cat, grab a snack, and when you get back, your loading days are drastically reduced.

(One of my fathers employees build a rig with a ramdisk and he can load BF4 maps in about 5-10 seconds.)