Ah sorry, fuel is usually the first thing to top out, and this happens around 240bhp - you'll need a fuel pump and injector upgrade at this point. Then the turbo will start to run out of puff, and this will need upgrading 250bhp is a practical limit on most stock turbos, before they start to whine, smoke and fail.
There are stage 1 turbos around for the similar OM612 with upgraded bearings and over sized compressor wheel for around 270bhp then if you want more than 300bhp you'll need at least a 2260 compressor wheel with extended tips.
The Mercedes engine parts are more readily available than Ssangyong parts, so these are a good place to start when looking for upgrades but you start to wander into uncharted waters.
I'm always amazed that a remap will give around 40bhp more power and improve fuel economy by around 13% on these engines.