I'm doing my best to launch an SSTO into orbit. Currently, my primary objective is to replace my LVT-30 with an LV-909 so that I can reap the d/v rewards. Unfortunately that means pushing as high and as fast with the airbreathing engines as possible.
I seem to have hit a brick wall at 1400 horizontal meters per second. No matter what I do, my craft won't beat that speed. Levelling off soon enough to have enough air to push faster means too much drag and the plane explodes.
I added More Engines™ but only managed to increase to 1456m/s. I've managed to hold that speed for several minutes now at about 10km alt but can't break it- the craft doesn't explode but no longer accelerates.