So yeah the booster came from Cruella and I reduced the tanking (parts that ain't using) and it flies near 6.8k m/s then the shuttle goes with frontier instead of titan (I like brute thrust but I I rather conserve propellants there)
OH plus thing its uh.... rather unstable for now (flips very erratic once on 38km alt) so I'll slap a bunch of torque n cold gas to counteract it (haven't done that part yet)