Two completely contrasting opinions Nismo do you have a load of apps open in the background?
I have the 4 and I'm not even going to bother with ios7, my phone is slow enough as it is
Yes updated to ios7 last night on my iphone 4 and mostly all good so far
Perhaps slightly slower but certainly not annoyingly so
Only annoyance for me is loss of Podcasts in "music"
Yas, see my comment above. It seems to me a slow iphone 4 (on iOS 6) is just due to build up of crap over time. A factory reset really did the trick for me and I actually have no complaints about the 4 (coming from a Nokia 820).