Swapping Rear Derailleurs
So... this might be dumb but I got a nearly-new Dura-Ace 10 spd rear der and I put it on a bike that originally had a Sora component. 8 spd.
How bad is this going to screw the pooch or am I just worrying excessively?
Just do it.
Your shifting quality will have more to do with how well you do the adjustment than Sora vs. Dura-Ace. The absolute worst thing that can happen is you'll hate it and you can put your sora derailleur back on. Even if it comes to that it still won't have been a waste because you will have learned by going through the process.
Go for it, or sell the derailleur and buy yourself something else. Sounds like a win, win to me.
Well the Sora was damaged in an accident with a half-inch think treebranch and hasn't been the same since.
I was just more worried about the chain size/cog spacing difference between an 8 spd and a 10 spd.
But, we'll see.