GG Nightlight torso length - I've used this pad in the Conduit's sleeve, but it's an uncomfortably tight fight. I've yet to perform surgery on my pad like Jason Smith describes in this thread, but I may give it a try some day. I found the pad to work great--not too stiff, comfortable against the back--but I never carried more than 12 pounds (6 pound base), so I don't know how much weight it could handle before beginning to collapse.
The tight fit led me to try another pad: BMW's Torsolite. If you can wait for a new shipment or find one used, it might be worth it. The pad, while heavy by SUL standards, is amazingly comfortable, durable, and, dare I say, attractive. It also worked perfectly for me folded up and inflated in the Conduit's pad sleeve, again keeping in mind that I never had a heavy load that might have collapsed the virtual frame.
In the end, I would advise getting the GG Nightlight torso if spending the $16 isn't much of a financial burden for you because it's a great foam pad for when you really want to drop some weight from your pack, go as simple as possible, and still be pretty comfortable. It will probably work very well as a virtual frame in almost any UL pack, including, with a little bit of post-purchase hacking, a Conduit.
Then, try it, see if you like it. And if you want to step up to some luxury at the cost of approximately 6.5 ounces, buy a Torsolite as soon as they become available.