I use a BA Mystic SL, which is cut the same as the Lost Ranger. Last year, I upgraded from my very old, orange Thermarest to a Big Agnes Insulated Air Core in the 20" wide, long. It's excellent to sleep on and I easily inflate it with the Instaflator from Leslie Pools.
Back in Mammoth after a trip, we saw the 20" wide, Long Q-Core, the grey one, at Kittridge. They had the regular BA's just like mine and another hikers, so we layed them down and compared with them on the hard floor. The Q-core is noticably awesome.
At REI, I laid the Q-Core SL 20" over the top of a grey Q-core 20". The SL is at least 2 inches narrower and hits my body at the shoulder blades. I couldn't find the "wide" to try to stuff into the BA bag sleeve, but I can tell you: the so-called 20" SL is a terrible, bad joke. If you're looking for a very comfortable pad, do go lay on the regular grey Q core.