Allow capacity per stream
Streaming services adapt quality to the available connection, but higher resolutions need more sustained downstream capacity. A single HD stream is relatively modest; several simultaneous 4K streams require much more headroom.
Stability prevents buffering
A connection that repeatedly drops below the video bitrate can cause buffering or quality changes. Strong Wi-Fi coverage and consistent throughput can therefore matter more than one short peak speed test.
Plan for the whole household
Add the likely demand from televisions, tablets, game downloads, video meetings and cloud services. Leave headroom instead of choosing a package that only just meets the theoretical total.
Troubleshooting streaming problems
Test close to the router, compare Ethernet where possible and check whether other devices are downloading heavily. If only one streaming device struggles, its Wi-Fi capability or placement may be the limiting factor.