Here are some images from various boats backstays. As you can see, there are many mousetraps out there.
Old School -
I have a 48:1 above deck system, attached to a 5mm Dynex Dux backstay. The initial 2:1 is also Dux, while the remaining line is all 1/4 or 3/16 spectra. The final 2:1 (red in the picture) is about nine feet off the deck, so this will give me maximum 2.5 inches of actual movement. I probably only use about 2 inches in reality. I have no idea of what this equates to in tension, but I can say that it puts a nice hook in the mast.
I used the ferrules a bit differently from what you usually see. For the primary ferrule (top), I spliced the backstay through the hole, ran the 2:1 around the groove, and the final 2:1 through the hole as well. For the secondary ferrule, I did much the same thing, but used it as a single block with becket. As I realize this image might not really demonstrate the system well, here is a diagram of it:
Surfer Girl also has a 48:1, but is more compact, is a two-speed system, and uses the cockpit drains.