It sounds like your Sora front derailleur is not set up correctly. Old Bobcat and/or the shimaNO tech doc web page can get you headed in the right direction. There are some very important details that need to be followed when setting up and dialing in shimaNO derailleurs.
In thinking about upgrading to a 105 (or any other changer for that matter) front derailleur, make sure it is compatible with your shift levers or you will have to upgrade those, also. The 105, when properly set up is a decent unit. It's not the most rapid shifting changer, but it is very solid and accurate.
In thinking about upgrading to a 105 (or any other changer for that matter) front derailleur, make sure it is compatible with your shift levers or you will have to upgrade those, also. The 105, when properly set up is a decent unit. It's not the most rapid shifting changer, but it is very solid and accurate.