It's not officially supported, but the X3480 is, but it needs bios version F5 while the i5 only needs F2.
http://www.gigabyte.fr/Motherboard/GA-P55-USB3-rev-10#support-cpu
Ryzen's supported memory speeds can vary according to the number of sticks you have installed.
http://www.guru3d.com/articles-pages/amd-ryzen-7-1800x-processor-review,13.html
In gaming, it helps in scenarios where you are cpu limited and some titles that really seem to like a lot of memory bandwidth, but with most games that are gpu limited, you won't notice any difference.
Linus said in a video that they upscale their video to 4k from 1080p, because then youtube will compress it to higher bitrate then if they had uploaded the same thing in 1080p.
Most likely a placeholder price, if someone managed to buy it, it would be easier to refund the excess rather than to charge more if it was too low. Anyway, we'll surely find out tonight.