All of the kits are upgradeable. Everyone is different on how much power they feel is enough, some upgrade over time and other stay with what they originally decided on. I have had every version of kit in my personal M3 and they are all great in their own way. Im currently running the VT1-535 and find that the car has great balance. The high HP VT2 kits can take the car to crazy fast if that is what you desire