Syncthing crippling internet speeds?

Another office started a large image transfer so has given me a chance to see if the speed issue is there, it is.

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so I enabled throttling at the receiving end to 900 to see if it would slow down the requesting data…

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but made no difference. So paused the sync and retested the speed…

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Can anyone think of a tool I can use that will look at realtime transfer speed on the quic protocol?