400 is a big investment, I bought a power commander fitted it and used one of the custom maps of this website and the difference is massive! Almost zero surging so far but I will have to take it for a longer ride out to be sure. You won't regret getting one as I was almost at the point where I was going to sell the bike as the surging was so bad. I use my bike for commuting through town everyday so I'm always in that low rev range doin about 30mph.