You need to better define "freezes up the Internet connection", what exactly happens? Can't open new connections but the existing ones work fine? Can you ping the firewall, its WAN IP, its WAN default gateway, Google, …? Torrent problems aren't common, they're far less common here than with your typical Linksys because they can't handle large numbers of connections generally.
If you have settings in your torrent client that let it go crazy with creating large numbers of connections, you may be maxing out your state table. You can check that on the front page of the web interface, and in the RRD graphs, and can increase it under System>Advanced.