Can make a trip from Gleba to Nauvis and back, with dropping off cargo, in 42 seconds. Want to minimize time the science packs can spoil.
Heard a ship's top speed is based on it's width, so here is the minimum width ship. Uses 8 thrusters to break 1,000km/s, but you could extend it infinitely. Even with 1 Thruster it was still going pretty fast.
There's no reason you couldn't add red ammo or rockets / rocket turrets to it either if you wanted it to go to Aquilo. You'd just have to keep extending the ship vertically.