Maybe. What's more important is the signal strength you get in that location.
Note that the Roku Ultra description mentions "fast" and mentions "best Wi-Fi" but nowhere does it say "fasted WiFi." If you're getting 25 Mbps consistently to a streaming device (Roku or other) then you'll be able to stream UHD/4K without issue. Anything faster won't make a difference.
DBDukes Roku Community Streaming Expert Note: I am not a Roku employee.
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