It seems that while LQ has quite a bit of reviews, I can't seem to find any way to utilize that info without knowing what I'm looking for first.
This would lead me to suggest my personal favorite: http://distrowatch.com/search.php
This will give you a page with a bunch of checkboxes to narrow down what you need out of a distro.
I would suggest using the "Distribution Category" checkboxes to look through Old Computers, Specialist, and Thin Client if you have very strict hardware requirements for your vm instances.
However, avoid the No Desktop checkbox as that will only show distros with absolutely no desktop available by default and rule out distros you can simply choose to not install a desktop.
Also, consider a server like implementation of any OS of your choice. A good example is to use Debian and not install the Desktop package. You could even leave out all major packages and only install the base system and use apt or aptitude to get you a torrent client/server with the necessary dependencies. I'm not sure which of these you are aiming for, a server farm, or a peer swarm.
Finally, if you just want something fast to deploy that's reasonably tested with little variance to setup, I would suggest something like Damn Small Linux (which you'd find listed on DistroWatch with many other minimals) that is a complete system with very little resources needed for storage or operation. These miminals might not come with a BT client/server, but most have a package management system, such as DSL's MyDSL. So you could install a full system fast with little effort even from an image, and simply get a package or two that you need.