Lets be honest here, formations are all well and good, but if players are static they don't mean much. The most impressive thing against Arsenal imo was the movement off the ball.
When we were defending the closing down of Arsenal was as good as I've ever seen it from us. Their players are usually so good on the ball, so for us to fluster them is superb, and that kind of defence so high up the pitch will do the vast majority of teams in the league. As we saw with Arsenal though, the challenge is keeping it up for 90 minutes.
The movement when we have the ball is equally good. I mean Jags and Distin haven't become Beckenbaur over night, but they, and to a large degree Howard too, are playing from the back now because they have options to pass to. That is going on throughout the team and is resulting in the sexy play we see.