You are confusing the purpose of a Roku player. It's designed for streaming from the Internet. From such sources, nothing streams at a bitrate beyond about 20 Mbps, which is more than satisfactory on Fast Ethernet.
Yes, your Roku can play media ripped from DVDs and Blu Ray discs. That said, it's limited in support for some audio and video codecs, so not all ripped media is playable. Your Roku really isn't the best choice for that sort of media. For example, if your ripped media includes Dolby TrueHD or DTS Master Audio (which the vast majority of Blu Ray discs use), the Roku cannot bitstream the audio. It either must be transcoded by a server or the Roku must convert the audio (which the Ultra 4800/4802 can do in a limited fashion).
It is possible to play a ripped 4K movie on your Roku Ultra. But you have to use WiFi (802.11ac) instead of Ethernet. The best connection speed I have recorded with my Ultra 4800 is about 220 Mbps, which is enough to stream my UHD movies from my DLNA server, only transcoding the audio to basic Dolby Digital at the server. That upper speed appears to be a hardware limit, as I can't even play a 250 Mbps video clip directly from a USB stick.
There is really only one option for a player that has a Gigabit Ethernet jack that can play those local media 4K files without converting anything, and that is the Nvidia Shield. That device is now four years old, and so far Nvidia hasn't announced any plans for a new version. You can get a Gigabit Ethernet adapter that works with a Fire TV player, but it will have the same audio bitstreaming limitation as the Roku. I believe the Apple TV also offers an option for Gigabit Ethernet via an adapter, but it too has the same audio bitstream limits.
Dan
Roku Community Streaming Expert
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