Is there a sort of cap on simultaneous downloads?

[Norse10]

I'm downloading hundreds of movies (I have 300Mbps so that's not the problem) and notice that when I increase the max number of active downloads it seems to slow the speed. What I did was to increase max downloads to 200, increased global max connections to 10000 and max number of connections per torrent to 50. This seemed to be too much for Bittorrent to handle (it almost seemed like it got confused, and jumped around between the files, downloading a little here and a little there). I now have it at 25 simultaneous downloads, 200 global max, and 25 per torrent. This seems to work, but I don't get speeds above 10-15Mbps (total for all files), that's the reason I wanted the increase the number of downloads. It could of course be the ISP that limits bandwidth for VPN, but they denies it, and speedtest shows speeds of around 100Mbps both ways (can't expect much more with VPN). Speedtest without VPN shows in access of 300Mbps. I also moved the torrents to different HDD, so they are now spread over 3 different physical drives, to be certain that disk r/w isn't a problem.