If your current processor can handle games ok now, why are you looking to change to ryzen?
From a cpu point of view, you still have some cpu power in reserve via overclocking.
Try this test:
Run YOUR games, but lower your resolution and eye candy.
If your FPS increases, it indicates that your cpu is strong enough to drive a better graphics configuration.
If your FPS stays the same, you are likely more cpu limited.
As to your original question, the 2400 speed that your motherboard supports is the speed at which you can run without overclocking. All ram will boot at the slowest speed to allow you to get into the bios where you can configure higher speeds. Selecting a higher speed XMP profile is the usual way.
Your motherboard can support ram as fast as 4133 when overclocked.
Here is an older study on ram speed scaling:
http://www.silentpcreview.com/article1478-page1.html
The net is that the difference between slow and fast ram is negligible, on the order of 1% for gamers using a discrete graphics card.
Should you go ahead and order fast ram with the intent of buying a future AM4 motherboard, restrict your choices to ram on your prospective motherboard QVL list.
Not all DDR4 ram will otherwise be compatible.
Most games do not take effective advantage of more than 4 threads.
You have a 8 thread upgrade available on your current setup with a i7-7700K.
The big advantage of ryzen is for the many cheap threads.
They are largely overclocked out of the box and faster than 4.2 is unlikely, and only from the better binned X suffix versions.
If your use is for multithreaded production, then ryzen is very good.
For pure gaming, Intel is still best, but by a decreasing margin.