By "freeze", I mean that the entire VM window's contents stops refreshing, any audio playing on the guest skips, and the guest ignores keyboard and mouse input. If I notice quickly enough, I'm able to use the Machine menu to reset the VM; else, the VM window also becomes non responsive, and the menus ghost and display sluggishly.
If I remove the port forwarding, this problem doesn't seem to occur (although I haven't tested this scenario with a large variety of torrents), which supports my theory of high network load causing the freeze (without port forwarding the download speed is significantly slower).
I've just completed a torrent in Azureus by ensuring that it's the only one running, setting "Max simultaneous outbound connection attempts" to 4 (neither 8 nor 6 worked), and reducing the MTU right down to 1300. Whether or not this luck continues, remains to be seen.
I've heard of BitTorrent crashing some home routers before, so I'm assuming that VirtualBox's network card is simply buckling under the strain of so much network activity. I've ruled out the host's network card/router.
Is this issue known? If not, I'm happy to provide debugging information if somebody could point me in the right direction. This is the first (and hopefully the last) time I've used Windows in a decade, however, so I'm not familiar with troubleshooting it -- I may need diagrams.
