Will an Ultegra rd work with a Sora shifter?
 

I just picked a used Bianchi Via Nirone 7 with Sora group. I have an Ultegra rd that I'd like to put in the bike so as to upgrade the drive train a bit. Is this doable?

Yes, Shimano road rear derailleurs (with the rare exception of pre-9-speed Dura Ace) are compatible with all of their road, (and most of their MTB) indexing shifters.

Word.

Don't expect an order of magnitude improvement from the change. Properly set up, all of Shimano's stuff does a fine job so unless your current derailleur is defective the new one should shift similarly.

So unless I'm upgrading the whole drive train, maybe I should just dance with the one that brought me.....

Or realize that prettier girl you took home isn't any better once the lights are out. :)

Like the rest of the guys here, I just figured she would look better hanging off my bike....

If there's more than one "speed" difference, derailleru cage might be too narrow for the chain e.g. 10 speed ultergra der with an 8 speed Sora chain and cogs, might rub. While one "speed" difference usually isn't a problem.