If all you do is gaming, in general, you are fine on your processor. New Intel is faster, but not by so much in games. It depends on each game optimisation and last TW games were somehow poor on AMD processors, especially at launch.
As for ddr4, its impact in gaming are negligible compared to ddr3. That is the last reason to upgrade. It seems ram is already fast enough compared to the other components so that higher speed does not matter. It may in the future, but so far, for gaming, it is not the most important investment.
With your system you will be ok. Remember, badly optimised games are a poor reason to waste money. And CA does this a lot with its games. On the other hand you spend more, you will have somehow better results. Also to note that there is some AMD help in building this game.
New mobos bring good things to the table, including support for new technologies of connecting SSDs (m.2 for example), but, same as ddr4, will not impact your gaming performance at all.
In conclusion, moving to Intel will turn well in big battles where more processor power is needed, also in some day to day tasks in programs that use only one thread. But in most games and most of the time in TW, the gpu is the one that is used to the max and this is a trend that will continue in the industry despite all the talk with DirectX 12. Eventually you will have to move on from your FX proc but dont expect miracles in badly optimised games. Take your time, find a good upgrade path and dont be afraid that the AMD proc will let you down too much until then. Both 4790k and 6700k are great. Depending what you do on the computer 5820k on X99 platform could be better. Or the upcoming Zen (amd) and Kabylake (intel). Or just accept a strategy game does not need 60 fps and take a vacation with your significant other
posting a little late
Yes. Most of the time you wont see a big improvement even with an i7. Despite the fact that in theory new Intel can get to about 40% bonus in single threaded work. But difference in games between i5 and i7 (usually none at all) is smaller than between FX and i5 (usually 10%).