A hypothetical question - traffic?

I scan my system with all the recommended anti-rootkit tools regularly, but since rootkits can easily make one paranoid, I was wondering about something.

I am in a shared network which caps upload speed; whenever there is an upload going out from me, my download speed will drop instantly. The higher the upload rate, the quicker the download rate will crawl down.

Now, assuming that there was something undetectable by any programs at the moment, I think (hope?) that if/when it tried to contact its control host to, say, upload some stolen files, keylogs, or try spamming, etc., as most of this trash is used to do - then I would notice the instant drop of download speed on my side because the external network filters would kick in, even though traffic monitors ran on the affected system would presumably not show any outgoing packets...?