I currently have a low quality Shimano Acera on my Trek 4100 and it´s really starting to annoy me when I want to change gears going up hills. I can never anything close to crisp in the shift. So I was considering anything better, LX, XT, even an XTR. But the problem is that they are all 9 speed. Would I need to get a new cassete or hubs or a new chain, if I wanted just to change the derailleur? Could I just run the 9 speed in 7 speed?
Edit: Or could something like this be a good solution?