Regarding this, is it OK to overclock RAM?
Overclocking your RAM is fine - increasing the frequency won't have any ill effects on the modules. However, excessive voltage on the RAM is not safe as that will shorten the life-span of the modules and could burn out the memory controller.
Beside above, how much can you overclock memory? Memory tweaking tipsMost DDR3 RAM runs at 1,333MHz, but overclocking RAM such as G. Skill's RipJawsX will happily run at 2,133MHz. Ramp it up incrementally, though. If your PC boots, restart it and increase the frequency some more.
Simply so, can I overclock 2400MHz RAM?
If not, that's a huge overclock and it's unlikely that any 2400MHz RAM will be able to handle it. The RAM you linked to is 2400MHz and it says right in the description that the maximum clock setting it can handle is 2666MHz, so the answer is no.
Does RAM speed affect FPS?
RAM is core not just to the system as a whole, but even to components like the best graphics cards. Your RAM isn't going to affect your processor's speed or the transfer rate of your storage drives.