I would have just replied on Cancel in-progress download when an upgrade is grabbed but that thread is locked now. I’m starting a new thread as I believe my suggestion addresses the reason that thread was closed.
I agree with the basis of that thread. If Sonarr finds an upgrade for a release while a release is being downloaded, the upgraded release should be queued to the download client and the (lower scoring, currently downloading) existing release on the download client should be paused, and the upgraded release’s download started. If the upgraded release’s download succeeds, the previous (now paused) download should be cancelled. If the upgrade fails, the previous download should be resumed.
Otherwise there’s little (from a download bandwidth/capacity) point to upgrading releases. In fact downloading both releases actually becomes a penalty as you download one that will be discarded increasing one’s download costs, not decreasing them.
If you are downloading from usenet and paying per byte downloaded, or downloading on a metered Internet connection, this ends up being an unnecessary usenet and/or Internet cost.