Flew back to Deciat last night and changed the thrusters to drive distributors, which sent me well over 800 m/s boost. Four-pip cruise is 600. That's unarmed though.
I had an overcharged 2A power plant in storage, so made that swap and added thermal spread to it. Lightweighted the life support after unlocking Lori Jameson and made a few other small mass-saving upgrades. It's getting there. This ship cruises faster than any of my other ships boost