I made the switch from 6.1.2 to 7.1.1.
It did not feel bad at all, at least to me. I have not tried how bad it was when it was 7.0.4.
Comparing 6.1.2 to 7.1.1, I personally feel it is a worthwhile upgrade. My old 6.1.2 JB was really slow and bogged down. The new apps are not working smoothly with iOS6 and took ages to load.
Now on 7.1.1, it loads a little bit faster.
Some things to note is that I set up the phone as a new one, restarting from scratch. Also picked those settings to help reduce the fancful effects. So far so good.
Battery life seems terrible...but heck its a 4 year phone already. But on 2G, the phone is decent in remaining standby of around 10h. Usage hours is around 4-5h?