Getting up to 1200 m/s is probably the fastest I've got, without adding in rocket engines. Also I'm not sure how I feel about rapiers because they just eat fuel. I did try replacing a few jet engines with rapiers, but I don't think it did much for me. Edit: Just from some testing, it takes 175x4 thrust at a 45 degree angle to keep my ship from diving back to earth at 20km (going about 600-650m/s). About 130x4 thrust at 45 degrees to keep me up at 25km (going about 750-800m/s). At 25km I'm lacking the air to keep the engines at the required thrust. That is 4 super sonic jets at about 75% thrust, maybe 70%. I can maintain 120 out of the 4 engines at that height, but it's just not quite enough. Is it worth adding a few extra intakes that I toggle at high altitudes?