I've been trying to make SSTOs for quite the while, some successful, the vast majority not. What I have discovered however, is how easy it can be to make stock planes go excruciatingly fast at low altitudes. Iirc, my fastest plane @10km was a near-orbital bomber project that had been partly, maybe halfway, drained of fuel that went 2104m/s or something like that. It burned to a crisp soon after doing so (at least it was unmanned!) but it was cool to see that it would at least go over 2