I propose the hydrogen cyanide - fluorine rocket.
It has the fabulous potential for a vacuum Isp of up to 380s, with a propellant mix density of 1023 kg/m^3, handily beating methalox mixes. It is non-cryogenic and burns at over 4000K.
Exhaust is 43.3% hydrogen fluoride.
CNSA about to Paperclip this guy! Such an effective way to increase collateral damage from routine launches!