Managed to get up to 852 m/s with this one. Was using mechjeb at the time to keep it stable just because I was busy and didnt feel like babysitting it while it flew faster and faster in a straight line. As an added bonus, it lands pretty well too when it is out of gas. Though in this case I had to ditch it in the water. It would go quite a bit faster if i were truly watching it as I lost a good bit of gas and speed at one point when I stopped paying attention to how mechjeb was flying and ended up at 20,000m. Probably not good enough for first place, but faster then this at least.