Oostal, The Sora and Tiagra are improvements over the groups they replaced (RSX, RX100), but still not at 600 tri color level, IMHO. Much of how the 600 shifters work will depend on their condition and previous owner's care so it's quite possible your Tiagra shifters will be better than these 600 shifters. To swap you'd also need a 8S cassette. You can buy them to have a matched full group, but save the Tiagra stuff.
Brad