We have done fork lift on two previous bots and are very comfortable wth the results of the second year's bot, 2008. We used 3/32 cable and you can see in the first pic that we designed our own pullies because of the problem we had in the first forklift model. We made a recess to accommodate a bearing with a 1/4 in. bore in a small block of acetal (Delrin) and wrapped it in sheet metal. We then drilled an entry and exit hole in the Delrin for the cable and a 1/4 in hole through the side for a bolt for the bearing to ride on.
For the winch we used two FP's with a drum. Please note that you will ABSOLUTELY need a tension take up on the cable between the first pulley and the drum. If the slides are lubricated enough, you shouldn't need to close the loop (which just adds to the weight and headaches), gravity worked well enough for us.
If you'd like more detailed support, feel free to send a private message and I'll send you detailed pics if you'd like.
BTW, that forklift went to 11.5' in under 5 seconds