I doubt 10mA would kill you unless you were really unlucky.
The short circuit current of the 2.4kV capacitor will be 1/8th of the 300V 800µF capacitor because of Ohm's law. Not that this matters because it's not the impedance of the capacitor that'll limit the current but the human body.
The 12.5µF capacitor charged to 2.4kV will cause a much higher current to flow than 10mA, probably a few Amps or higher for a split second.
The 12.5µF charged to 2.4kV is much more dangerous, because a higher voltage will cause more current to flow, the energy would be dumped into your body faster and more of the energy will effectively be transferred to your body.
300V is unlikely to kill you anyway, even if it's a steady DC supply, the current will also decay to a non-lethal although still painful level, when the voltage drops below about 100V or so and at this point not much more damage will be done. Still, a large capacitor charged to 300V is potentially lethal so you should exercise caution by discharging the capacitor using a suitable resistor before touching it.