I'm fixing up an old Cannondale road bike and am in need of a new rear derailleur, but am unsure of what I need. I've done all the googling I can handle on the subject and I'm still confused. I've copied my component specifications and pasted them below. I'm looking for something Shimano, middle of the road, willing to spend $40-70, but just SO much to choose from, gahh! Somebody help!